About
the author:
Dr. Haas is a physician and
surgeon. He graduated from the
When he was a general surgery
resident in
He has personal racing
experience in Formula Super Vee. He is his own Lamborghini and Ferrari as well
as Mercedes mechanic.
Chapter
One - Motor Oil 101
I think it is time to go over
passenger car automotive engine oils in detail. I will be writing several
articles to be published soon so I will try to get some of it out here. I feel
this is a very general topic for all car owners on this board.
This is a very difficult
topic to comprehend. Everybody including good mechanics think they are experts
in this field but few understand engine oils. Most of what I hear is the
opposite of the truth. It is however easy to see how people get mixed up as
there is always some truth to the misconception.
Please forgive me if I am too
wordy or even verbose at times. I will be redundant for certain. This will be
in areas that people have to hear things over and over again to get it right.
Some will never be able to understand these concepts unfortunately. I base my
thoughts on those whom I have been listening to in various automotive chat
rooms and discussion with mechanics. I will try to minimize technical terms and
be somewhat vague rather than exact. I will round and average numbers to make
the point simple rather than mathematically exact. Thickness has the same
meaning as viscosity. Viscosity is a measure of the resistance of a fluid
(liquid or gas) to flow. Fluids with high viscosity, such as molasses, flow
more slowly than those with low viscosity, such as water. Again, I am trying to
explain general principals as I know them.
The greatest confusion is
because of the way motor oils are labeled. It is an old system and is confusing
to many people. I know the person is confused when they say that a 0W-30 oil is
too thin for their engine because the old manual says to use 10W-30. This is
wrong.
More confusion occurs because
people think in terms of the oil thinning when it gets hot. They think this thinning with heat is the
problem with motor oil. It would be more correct to think that oil thickens
when it cools to room temperature and THIS is the problem. In fact this is the
problem. It is said that 90 percent of engine wear occurs at startup. If we are
interested in engine longevity then we should concentrate our attention at
reducing engine wear at startup.
Oils are chosen by the
manufacturer to give the right thickness at the normal operating temperature of
the engine. I will say this average oil temperature is 212 F, the boiling point
of water. On the track that temperature is up to 302F. It is important to
realize that these are two different operating environments and require
different oils.
I will discuss driving around
town first. Everything I say will be based on these conditions. At a later time
I will discuss track conditions. Everything I say will be as accurate as
possible without looking everything up and footnoting. I am trying to be
general not ultra specific.
One thing that is no longer
important is the ambient temperature. Older automotive owner manuals often
recommended one oil for the summer and another for the winter. This is still
necessary for air cooled engines but is no longer a consideration in
pressurized water cooled engines. These engine blocks are kept at around 212 F
all year round. The oil is around the same temperature as well. This allows for
a single weight oil all year round. Again, this is not the same as on the track
where the coolant temperature is slightly higher and the oil temperature is
much higher.
Please forget those numbers
on the oil can. They really should be letters as AW-M, BW-N or CW-P. The fact
that we are dealing with a system of numbers on the can makes people think that
they represent the viscosity of the oil inside the can. The problem is that the
viscosity of oil varies with its temperature. A “30” weight oil has a viscosity
of 30 at 302
F (150 C) and thickens to 10 at 212 F (100 C). It further thickens to a
viscosity of 100 at 104 F (40 C) and is too thick to measure at the freezing
point of 32 F ( 0 C ).
30 weight oil:
Temperature ( F
)....Thickness
302...........................3
212..........................10
104..........................100
32..........................250 (rough estimate)
The automotive designers
usually call for their engines to run at 212 F oil and water temperature with
an oil thickness of 10. This is the viscosity of the oil, not the weight as
labeled on the oil can. I want to stay away from those numbers as they are
confusing. We are talking about oil thickness, not oil can labeling. This will
be discussed later. Forget the numbers on that oil can for now. We are only
discussing the thickness of the oil that the engine requires during normal
operating conditions.
The engine is designed to run
at 212 F at all external temperatures from Alaska to Florida. You can get in
your car in Florida in September and drive zig-zag to Alaska arriving in
November. The best thing for your engine would be that it was never turned off,
you simply kept driving day and night. The oil thickness would be uniform, it
would always be 10. In a perfect world the oil thickness would be 10 at all
times and all temperatures.
If the thickness of oil was
10 when you got in your car in the morning and 10 while driving it would be
perfect. You would not have to warm up your engine. You could just get in the
car and step on the gas. There would be little wear and tear on your
engine, almost none. Unfortunately the world is not perfect.
The night before when you
drove home from work the car was up to
the correct operating temperature and the oil was the correct thickness, 10.
Over night the engine cooled to room temperature and the oil thickened. It is
75 F in the morning now (I do live in Florida). The oil thickness is now around
150. It is too thick to lubricate an engine designed to run with an oil having
a thickness of 10.
It is time to introduce the
concept of lubrication. Most believe that pressure = lubrication. This is
false. Flow = lubrication. If pressure was the thing that somehow lubricated
your engine then we would all be using 90 weight oil. Lubrication is used to
separate moving parts, to keep them from touching. There is a one to one
relationship between flow and separation. If you double the flow you will
double the separation pressure in a bearing. The pressure at the bearing
entrance is irrelevant.
In fact the relationship
between pressure and flow is in opposition. If you change your oil to a thicker
formula the pressure will go up. It goes up because the resistance to flow is
greater and in fact the flow must go down in order for the pressure to go up.
They are inversely related. Conversely if you choose a thinner oil then the
pressure will go down. This can only occur if the flow has increased.
It seems then that we should
all be using the thinnest oil money can buy. This is partly true. Let me use my
575 Ferrari Maranello as an example. I drive this car around town. The manual
of this car states the target pressure is 75 PSI at 6,000 RPM. The gold
standard is that all engines should have a pressure of 10 PSI for every 1,000
RPM of operation, not more, not less. After all, you do need some pressure to
move that oil along, but only enough pressure, not more. More pressure is not better,better;
it can only result from the impedance of oil flow. Remember that oil flow is
the only thing that does the lubricating.
Note that Ferrari is not
saying what thickness of oil to use. That can only be determined by
experimentation. My engine oil temperature is running around 185 F as I drive
around town on a hot Florida summer day. I have found that the thinnest oil I
can buy that is API / SAE certified is Mobil 1’s thinnest oil. Even with this
oil I get 80 PSI at 2,000 RPM. It is too thick for my application yet it is the
thinnest oil money can buy. If I was on a hot Florida track in mid-summer the
oil temperature would probably get up to 302 F. I will guess that the pressure
would only be 40 PSI at 6,000 RPM. The oil I am using would not meet the
requirement of 75 PSI at 6,000 RPM from Ferrari. I would have to choose a
thicker oil for this racing situation. The oil I use now would be too thin at
that very high temperature. (This is only partly true. Higher RPM running
engines use thinner and thinner oils to get more and more flow. I will discuss
this later).
High flow does more than
lubricate. It is one of the things used to cool the hottest parts of your
engine, the pistons, valve areas and bearings. This cooling effect is as
important as lubrication in your engine. If your engine is running hot use a
thinner oil. The flow will increase and so will the cooling. This is even more
important in the racing condition.
Let us go back to the Ferrari
manual. My older 550 Maranello only specified 5W-40 Shell Helix Ultra as the
oil to use in all conditions. This car was designed for racing. As it turns out
Ferrari now recognizes that not every owner races their cars. The newer 575
manual now states to use 0W-40 for around town situations even though Shell
does not make this oil in the Helix Ultra formulation at this writing. They
also recommend the 5W-40 by Shell if you insist on the Shell product. It is
also the recommended oil for most racing conditions.
Ferrari recommends Helix
Ultra Racing 10W-60 “for hot climate conditions racing type driving on tracks”.
Note that they now realize the difference between the daily urban driver like
me and the very different racing situation. These are widely different
circumstances. I want to emphasize that they only want you to use this oil
while racing in “hot climate conditions”. If you are racing in Watkins Glen up
north use the 5W-40. If you are racing in Sebring in the middle of the Florida
summer use the 10W-60. Around town in any climate, use the 0W-40.
It is time to dispel the
notion that 0W-30 oil is too thin when our manual calls for 10W-30. A 0W-30 is
always the better choice, always. The 0W-30 is not thinner. It is the same
thickness as the 10W-30 at operating temperatures. The difference is when you
turn your engine off for the night. Both oils thicken over the evening and
night. They both had a thickness, a viscosity of 10 when you got home and
turned your engine off. That was the perfect thickness for engine operation.
As cooling occurs and you
wake up ready to go back to work the next day the oils have gotten too thick
for your engine to lubricate properly. It is 75 F outside this morning. One oil
thickened to a viscosity of say 90. The other thickened to a viscosity of 40.
Both are too thick in the morning at startup. But 40 is better than 90. Your
engine wants the oil to have a thickness of 10 to work properly. You are better
off starting with the viscosity of 40 than the honey - like oil with a
viscosity of 90.
I repeat: More confusion
occurs because people think in terms of the oil thinning when it gets hot. They think this thinning with heat is the
problem with motor oil. It would be more correct to think that oil thickens
when it cools to room temperature and THIS is the problem. In fact this is the
problem.
This is the end of lesson
number one.
aehaas
Motor
Oil 102
Chapter
Ttwo. It gets more difficult.
We left off discussing that a
0W-30 weight oil is not thinner than a 10W-30 oil. They both have the same
thickness at operating temperature. The 0W-30 simply does not get as thick on
cooling as the 10W-30. Both are still way too thick
to lubricate an engine at startup.
I have heard several people
say that Porsche specifically prohibits a 0W-XX engine oil, that it is too
thin. Now here is the partial truth I spoke of earlier. We will discuss
multigrade oils. Earlier we said that a straight 30 weight oil has a thickness
of 10 at the normal operating temperature of your engine. The multigrade oils
0W-30 and 10W-30 also have a thickness of 10 at 212 F.
The difference is at 75 F,
your startup temperature in the morning.
Oil type... Thickness at 75
F...Thickness at 212 F
Straight 30......
250......................10
10W-30............100......................10
0W-30..............40 ......................10
Straight
10........30....................... 6
Now you can see that the
difference between the desired thickness your engine requires ( = 10 ) is
closest to the 0W-30 oil at startup. It is still too thick for normal
operation. But it does not have far to go before it warms up and thins to the
correct viscosity. Remember that most engine wear occurs at startup when the
oil is too thick to lubricate properly. It cannot flow and therefore cannot
lubricate. Most of the thick oil at startup actually goes through the bypass
valve back to the engine oil sump and not into your engine oil ways. This is
especially true when you really step on that gas pedal. You really need more
lubrication and you actually get less.
Note that a straight 10
weight oil is also too thick for your engine at startup. It has a thickness of
30. Yet at operating temperatures it is too thin having a thickness of 6. It
needs to be around 10. The oil companies have added viscosity index improvers
or VI to oils to solve this dilemma. They take a mineral based oil and add VI
improvers so that it does not thin as as much
when it gets hotter. Now instead of only having a thickness of 6 when hot it
has a thickness of 10, just as we need.
The penalty is the startup
thickness also goes up to 100. This is better than being up at 250 as a
straight 30 weight oil though. Oil with a startup thickness of 100 that becomes
the appropriate thickness of 10 when fully warmed up is called a 10W-30 weight
motor oil. This is NOT as thick as a straight 30 weight oil at startup and it
is NOT as thin as a straight 10 weight oil at full operating temperature.
The downside of a mineral
based multigrade oil is that this VI additive wears out over time and you end
up with the original straight 10 weight oil. It will go back to being too thin
when hot. It will have a thickness of 6 instead of 10. This may be why Porsche
(according to some people) does not want a 0W-30 but rather a 10W-30. If the VI
wears out the 0W-30 will ultimately be thinner, a straight 0 weight oil. When
the VI is used up in the 10W-30 oil it too is thinner. It goes back to a
straight 10 weight oil. They are both still too thick at startup, both of them.
The straight 0 weight oil, a 5 weight oil and a 10 weight oil are all too thick
at startup.
This is just theory however.
With normal oil change intervals the VI improver will not wear out and so the
problem does not really exist. In fact, oils do thin a little with use. This is
partly from dilution with blow by gasoline and partly from VI improvers being
used up. What is more interesting is that with further use motor oils actually
thicken and this is much worse than the minimal thinning that may have occurred
earlier.
Synthetic oils are a whole
different story. There is no VI improver added so there is nothing to wear out.
The actual oil molecules never wear out. You could almost use the same oil
forever. The problem is that there are other additives and they do get used up.
I suppose if there was a good way to keep oil clean you could just add a can of
additives every 6 months and just change the filter, never changing the oil.
When the additives wear out
in a synthetic oil it still has the same viscosity. It will not thin as a
mineral oil. The fear that some say Porsche has that oils thin when the VI runs
out is not applicable to these synthetic oils. These oils will always have the
correct thickness when hot and will still be too thick at startup as with all
oils of all types, regardless of the API / SAE viscosity rating.
Automotive engine
manufacturers know these principals of motor oils. They know there is thinning
or thickening that will occur. They take these things into account when they
write that owners manual. Mineral oil change recommendations will generally
include shorter time intervals than those of synthetic oils.
The reality is that motor
oils do not need to be changed because they thin with use. It is the eventual
thickening that limits the time you may keep oil in your engine. The limit is
both time itself (with no motor use) and/or mileage use.
End
of part two.
aehaas
Motor
Oil 103
Part
Three. You have a
synthetic mind.
Let us compare mineral and
synthetic oils. I will not talk about chemical but rather functional
differences. We discussed before how mineral oils are too thick at startup yet
too thin when hot. The viscosity was corrected with the hot engine by adding VI
improvers.
A 10W-30 multigrade mineral
based oil is made from a 10 weight oil and has VI improvers added to thicken
the product in a 212 F engine. It acts as a 30 weight oil when hot. It acts
more as a 10 weight oil at startup. I remind you that a 10 or 5 or 2 weight oil
is still too thick to provide lubrication at startup. They are all too thick at
startup. There is currently no engine oil thin enough to operate correctly at
startup. They all cause excessive wear at startup. Again, we are discussing the
needs of my single hypothetical engine for around town driving.
Oil type.. Thickness at 75 F
..Thickness at 212 F
Straight
30..........250....................10
10W-30...............100....................10
0W-30.................40.....................10
Straight 10..........30.....................6
Straight 5...........20.....................4
Straight 2...........15.....................3
Straight 0...........12.....................3 est.
A 10W-30 synthetic oil is
based on a 30 weight oil. This is unlike the counterpart mineral oil based on a
10 weight oil. There is no VI improver needed. The oil is already correct for
the normal operating temperature of 212 F. It has a thickness of 10 while you
drive to work. It will never thin yet has the same long term problem as the
mineral based oil. They both thicken with extended age.
Synthetic oils are derived in
the laboratory. They are pure, usually nearly clear. I describe mineral based
motor oils as a distilled, concentrated product. The impurities need to be
removed from the raw petroleum. These oils are therefore less clean and contain
many impurities. Again, the problem is really more of theory than practice but
the difference does exist.
People repeatedly say that
synthetic oils are more stable in a hot engine. I hear that they lubricate
better. The answer is yes and no. Oil molecules do not break down, just the
additives. Generally, the synthetic oils do not have VI improvers so have less
to lose.
There are some properties of
synthetic oils that actually result is less wear than with mineral oils. These
help increase your gas mileage as well. Due to a reduction of internal friction
of the synthetic oil your engine will run a bit cooler. Wear increases as
temperature increases, all other things being constant.
A main advantage that the
synthetic has over the mineral based oil is the ability to lubricate at
startup. Both types of oil have the same specifications at 104 F, 212 F and 302
F. It is the startup viscosity characteristics that separate these oils.
Synthetic oils do not thicken as much on cooling. They have better fluidity as
the temperature drops.
A synthetic oil that is
labeled as 10W-30 is less honey like as a mineral based 10W-30 motor oil at
startup. They both have a thickness of 10 at normal operating temperatures. At 75 F the synthetic is not as thick. At 32
F the difference between the two is even greater. At 0 F the mineral oil is
useless yet the synthetic works fairly well. Just keep the RPM to a minimum.
At temperatures below zero
you will not be able to start your car with mineral oils while the synthetic
oils may be used to -40 or - 50 F. Oils are so thick that the normal method of
viscosity measurement is not possible. Instead we measure if the oil can even
be pumped or poured. Again, we are only discussing a single category of oil,
the multigrade 10W-30 API / SAE grade.
I took an except from the web
about Mobil 1 oils. They compared a 5W-30 synthetic Mobil 1 oil to a mineral
based 10W-30 and a 10W-40 in ice cold conditions. The engine turned over at 152
RPM with the synthetic 5W-30 Mobil 1. The 10W-30 and 10W-40 mineral oils turned
over at 45 and 32 RPM respectively. Neither of those engines started.
Motor oil becomes permanently
thicker with exposure to northerly winter type weather. This is more of a
problem to mineral based oils. Waxes form. This is why it is a bad idea to even
store a bottle of oil in a cold garage. It goes bad on the garage self just
because it is exposed to the cold.
To recap, synthetic oils have
similar characteristics as mineral oils at operating temperatures. The
synthetic oil will however be less honey - like at startup even though it has
the same API / SAE rating. Yet the synthetic 10W-30 weight oil is based on a
heavier 30 weight oil while the mineral based 10W-30 oil is based on a thinner
10 weight oil. They are both similar at operating temperatures yet the 30
weight based synthetic is actually less thick at startup and much less honey -
like at low temperatures. This is the opposite of what common sense dictates.
This is worth repeating: The
synthetic 10W-30 weight oil is based on a heavier 30 weight oil while the
mineral based 10W-30 oil is based on a thinner 10 weight oil. They are both
similar at operating temperatures yet the 30 weight based synthetic is actually
less thick at startup and much less honey - like at low temperatures. This is
the opposite of what common sense dictates.
As one can see this is no
easy topic. Are you with me?
aehaas
Motor
Oil 104
Part
Four. It is not
what we thought.
Now let us finish talking
about the differences of mineral verses synthetic oils. I will compare the same
weigh or grade of oils showing that the operating viscosities are the same
whereas the startup viscosities vary:
Mineral oil:
Oil type...Thickness at 75 F... at 212 F...at
302 F
Straight
30..........250....................10..........3
10W-30...............100....................10..........3
0W-30..........There are none in this
range......
Synthetic oil:
Oil type...Thickness at 75 F... at 212 F...at
302 F
Straight
30...........100...................10...........3
10W-30.................75...................10...........3
0W-30...................40...................10...........3
Since the synthetic oil
thickens less on shutdown your startup will be easier and so will the stress on
your engine. This is perhaps the best thing the synthetic class has over the
mineral based oils.
People sometimes use a
thicker oil to minimize gasket leaks. This seems obvious to me. Repair the
gasket. Do not destroy your engine with an oil that is too thick for proper
function.
Some people have said they
use thicker oils because they only use their cars every 2, 3 or 4 weeks. They
are afraid that thin oils will fall off the engine parts and result in a lack
of lubrication at startup. Think about your lawn mower over the winter. It gets gummed up solid. The oil and
fuel thicken over time resulting in engine failure. Anyway, oil on the surface
of parts does not lubricate. It is the FLOW of oil between parts that lubricates.
Thick, old, waxy oil can only be bad.
I have seen several car owner
manuals that are now stating that oils do not need to be changed but every
7,500 miles or more. The same manual also states OR every 12 months, whichever
occurs first. My feeling is that you can probably go 5,000 miles on the average
(in a sports car) but you must change your oil in the spring time at a minimum,
particularly up north. Oils form waxes in icy cold weather. There is a
permanent thickening of the oil.
Some automotive manufacturers
are backing down on oil change intervals to 5,000 miles or less and some
advocate changing the oil at least every 6 months as well. I think this is
because of the tendency for oils to thicken in very hot engines (not ambient
conditions, just hot engines). Also because of thickening from the cold of
winter and from sludge build up that cannot be filtered out.
I truly believe that oil is
much better being too thin than too thick. Over the years we have been going to
thinner and thinner oils despite hotter engines with turbos and the like. The
tendency is that people figure they need a 40 weight oils but then use a 50
instead. Better thinking is that if you think you need a 40, use a 30 weight
oil instead. I firmly believe this based on all I know about oils.
As it turns out synthetic
oils do cling to parts better as they have higher film strength than mineral
oils. Synthetics are thinner overall. They have greater slipperiness. Yet they
stick better to engine parts. Again, this concept is the opposite of normal
thinking.
The thickness of moving oil
is measured in centiStokes or cS. Most engines want the oil viscosity to be
around 10 cS at normal operating temperature. The really thick multigrade oils
have a viscosity of 20 cS at operating temperature. One is not twice as thick
as the other, it is only 10 cS thicker.
As we increase the heat from
212 F to 302 F the most commonly recommended oil thins from 10 cS to 3 cS. The
thicker oil drops from 20 cS to 4 cS. Note that in a very hot engine the
difference between the two oils is now only 1 - 2 cS. In other words they have
about the same thickness. There is little advantage to a thicker based oil as a
20W-50 at very high temperatures. No, the 4 cS oil is not twice as thick as the
2 or 3 cS oil. This difference is almost insignificant.
There is a huge advantage of
using the thinner, 10W-30 at startup where 90 percent of the engine wear
occurs. At 75 F the thicker oil has a viscosity in the range of 250 cS while
the thinner oil has a viscosity of 100 cS. The thicker stuff is 150 cS thicker.
This is a very big difference. I am using the 20W-50 as my thicker oil example
here.
People are always asking
about adding things as Slick 50 into the oil tank. Do not do this. The oil
companies and engine manufacturers work together very hard to give you the
product you need. Engines are running hotter, longer with more BHP from less
CID. Smaller, more efficient engines are getting us more MPG and yet better
acceleration. These engines last longer and are more reliable.
Part of that reason is the
nature of the lubricants. There is a lot of competition to get us the best
working motor oil. Independent additives cannot make the oil better and in many
cases makes things worse. There have been engine failures as a result of adding
some of these aftermarket additives to
motor oil.
Motor oil that is labeled for
RACING ONLY is not usable for every day driving. Often these have more
additives that are toxic to your catalytic converters and the environment.
These oils generally do not have detergents. These are very important for your
engine unless you plan on taking it apart every few weeks and cleaning every
single surface. The oils do not meet the API / SAE requirements for ratings as
SJ, SL or now SM.
You do not need to use the
exact oil type and brand that your car manual tells you to use. Oils are pretty
general. They are not that different. Ferrari is married to Shell. If you call
them up and ask to use Valvoline instead they will tell you that they have not
tested that brand in their cars. They only tested the engine with Shell oils.
They cannot comment on the performance of other oils in their engines. This is
a fair statement. The reality is that the Shell and Valvoline oils of the same
specification (viscosity, API and SAE ratings, synthetic or not) are very
similar. ( I do have my bullet proof vest on ).
People often say that their
old 1980 car manual says to use a specific Brand-X motor oil. They keep trying
to locate these older oils. First, just about any oil brand that meets the
original specifications will do. Second, all oils are much, much better now.
They are all much better. One could say that synthetic oils are better than
mineral oils but is is hard to say that one brand is that
much better than any other. Personally, I do stick to the big names. It does
not mean that small motor oil companies are not as good. They could be better
for all I know.
Using an oil that is less
thick at startup has other benefits. Let us compare a synthetic 10W-30 to a mineral
based 10W-30. Both give you a viscosity of 10 cS at normal engine operating
temperatures. They both thin to 3 cS at high temperatures. At 75 F tomorrow
morning the story will be different. The startup viscosity of the synthetic
will be 50 whereas the mineral based 10W-30 will be 75. Again, both are too
thick at startup but the synthetic will cause less startup time period wear and
tear. You will get a little better gas mileage too.
The synthetic lubricated
engine will turn over easier. This has the effect of using less power from your
starter motor. It will last longer. Your battery has less of a current draw.
This will also last longer. The battery was discharged less during the start so
the alternator will rob less power from your engine to recharge. The alternator
lasts longer and you get a little better gas economy. The only downside of
synthetic lubricants is the cost. They cost 2 or 3 times as much as mineral
based oils. Never-the-less I use plain Pennzoil multigrade mineral based 5W-20
in my Ford Expedition. This oil is thin enough at startup to have many of the
attributes I just mentioned.
aehaas
Motor
Oil 105
Part
Five. Let’s use top
gear:
Let’s go racing. I will
discuss driving in traffic jams in the
On the race track one usually
uses all the BHP their engine can give them. You briefly step on the brakes for
the corner then put the pedal to the metal the rest of the time. Your oil will
get up to 302 F, but your cooling system is around 212 F. The engine produces
tremendous heat but can only pass it off so fast to the cooling system. There
is a lot of air moving past the cooling radiator so the antifreeze / coolant is
able to get rid of the extra heat from this part of the system with relative
ease.
The temperature of oil on
your gauge is not as hot as it really gets. This temperature is an average with
oil from different parts of the motor. Some parts are hotter than others. It is
said that some of the oil gets as hot as 400 or 500 F in these racing
situations.
In an earlier section I said
that thicker oils are usually needed in racing situations but not necessarily.
Remember that a major function of oil is to cool the inside of your engine. In
ASTM D 4485 3.1.4: “Terminology: Engine oil- a liquid that reduces friction and
wear between moving parts within an engine, and also serves as a coolant.” Since the oil with a viscosity of 10 cS at 212
F thins to a viscosity of 3 cS at 302 F we will get more flow. The pressure
will go down some as well. This is OK as long as we have a minimum of pressure
to move the oil.
This increased flow will
result in increased cooling by the oil. This is a good thing. You would
probably want more oil flow in these situations and you get it. The hotter oil
thins and this increases flow. The higher flow works harder to separate the
engine parts that are under very high stress. It all works out for the better.
Higher revving engines need thinner oils. You do not necessarily need to go to
a thicker oil while racing. Only experimentation will tell.
The best way to figure out
what viscosity of oil you need is to drive the car in the conditions you will
use. Then use the oil viscosity that gives you 10 PSI per 1,000 RPM under those
circumstances. For some reason very few people are able to get this simple
principal correct. I cannot explain further.
These same rules apply to
engines of any age, loose or tight. Just because your engine is old does not
mean it needs a thicker oil. It will need a thicker oil only if it is overly
worn, whether new or old. Yet the same principals of 10 PSI per 1,000 RPM still
apply. In all cases you need to try different weight oils and see what happens.
Then choose the correct viscosity.
I am using 0W-20 in my
Ferrari 575 Maranello right now. It has over 5,000 miles on the clock. There
will be a day (my estimate is 50,000 miles) when I will have to go to a 0W-30.
In the future I will have to increase the viscosity to a 0W-40, then a 0W-50,
maybe. I will use whatever it takes to give me 75 PSI at 6,000 RPM during the
lifetime of my engine. This formula works in all situations.
Some people have tried this
and occasionally get a somewhat low oil pressure while at idle. This is fine.
There is no stress on parts at idle, the smallest oil flow will do the trick.
It is at higher RPM where more BHP is produced. This is where we need the flow.
Remember that Ferrari uses 75 PSI at 6,000 RPM as the place to test your oil
viscosity needs. If your oil gives this value under your driving conditions
then your lubrication system has been maximized. Period.
Do not go 5,000 miles with
the same oil if you are racing your car. You should change the oil every 1 or
2,000 miles. If you drive your car around town then you need to change the oil
for that situation. Use racing oil on the track and urban oil around town. The
best situation as described by Ferrari is to use the 0W-40 around town and the
10W-60 “racing oil” on the track. It has to be that “hot” track though. A
compromise situation would be to use the 5W-40 for both but this may not be
optimal. Certainly, if you are just an urban driver as me use the 0W-40 or even
a thinner oil as I do in my Maranello. Again, I use the 0W-20.
FYI. The Formula 1 cars that
run at 15,000 RPM and higher use straight 5 and 10 weight oils.
Now let me discuss what
people think is a similar situation to racing. That is hot summer traffic jam
driving. Your car should be able to handle this. If you have problems then you
have a problem with your car, most likely in need of a cooling system overhaul.
When you drive that car down
the road mid-winter in upstate
Your engine is not producing
much heat at low RPM and low BHP output. The production of heat is relatively
slow. It can easily be transmitted to your cooling system. The problem is that
your cooling system has trouble getting rid of the heat. The oil and the
coolant will slowly rise in temperature. They both rise together. The increase
is no big deal for your oil. It goes to 220, then 230 F. The problem is that
the cooling system can only handle heat up to 230 F. After that you overheat
the cooling system and the car must be shut off. The oil never got that hot, It
was just that the water got a little hotter than its system design.
You now see that overheating
in traffic is a cooling system problem and not an oil system problem. Do not
change to a thicker oil based on your traffic situation.
aehaas
Motor
Oil 106
Part
Six. A personal
recommendation.
These are the motor oils I
recommend. This is based on information that I just happened to collect. I have
not gotten the specifications of all oils out there. My opinion on these oils
is based on viscosities. By this I mean less honey like at start up
temperatures and appropriate for the required viscosity at operating
temperature. I broke it down to two classes, 1-Fully Synthetic and 2-Mineral
(dinosaur) oils and blends of dinosaur and synthetic. The asterisk is my
preferred from each group of very similar products. And these are usually
easier to find in my experience. Remember, all oils are too thick at start up.
There is no such thing as an oil that is too thin below 100F. The thinnest
motor oil made is still too thick at start up temperatures.
It seems that many engines
work best with a multigrade 30 weight oil. Others would do better with a 20
weight oil and few would require a 40 weight oil. You can only determine what
is best by experimenting. Admittedly I did not think my Ferrari Maranello would
need a 20 weight oil. In truth I could actually use a 10 weight oil. A 0W-10 would be good but it simply does not exist
for normal use. Red Line does make 2W, 5W and 10W oils (this acts as a 0W-10
multigrade oil) but they are for racing only. One Formula 1 team has actually
used these very oils off the shelf from Red Line.
. Synthetic Class:
60 wt:
Redline straight 60 wt racing oil (racing
only, acts as a SAE 20W-60 oil)
Shell Helix Ultra Racing Oil 10W-60
Valvoline SynPower 20W-50*
50 wt:
Castrol Syntec 5W-50*
Shell Helix Ultra 15W-50
Penn Synthetic 5W-50
40 wt:
Mobil 1, 0W-40*
Shell Helix Ultra 5W-50
30 wt:
Mobil 1, 0W-30*
Penn Synthetic 5W-30
20 wt:
Mobil 1, 0W-20*
Valvoline SynPower 5W-20
. Non-Synthetic and Ssynthetic
blends:
60 wt:
Castrol Syntec Blend 20W-50
50 wt:
None recommended - all relatively too thick at
start up.
40 wt:
Penn regular Multigrade 10W-40
Valvoline Durablend 10W-40*
30 wt:
Penn regular Multigrade 5W-30*
Valvoline Durablend 5W-30
20 wt:
Penn regular Multigrade 5W-20*
Valvoline Durablend 5W-20
If while on the road you are
forced to add oil there are rules. Let us say for example that our engine has
synthetic Mobil One 0W-30.
Use the same type and brand
if you can. If you are using Mobil 1 then it is acceptable to mix different
grades but use a close grade when possible. It is not a good idea to mix say
1/2 your oil tank with 0W-30 and 1/2 with 15W-50 Mobil One.
If there is no Mobil 1
available then use mineral based oils next, preferably Mobil as first choice
then any other name brand next.
The last choice is to mix a
synthetic of another brand. They specifically say this should not be done.
I personally use Mobil 1,
0W-20 in the 575 Maranello and for the first oil change I drained the
Murcielago’s 5W-40 Agip and replaced it with 0W-30 Mobil 1. The engine became
much quieter. A valve tappet noise disappeared. I may try the 0W-20 next. For
all my other cars I use the regular Pennzoil Multigrade 5W-20.
You have to try by
experimentation what operating oil grade your engine requires. In all cases
however, you want the oil that gets least honey-like at startup.
aehaas
Motor
oil 107
Chapter
Seven. What is the
terminology from SAE and API.
Many think that the “W” in
10W-30 means “winter”.
From SAE J300 p.2:
"Two series of viscosity grades are
defined in Table (1): (a) those containing the letter W and (b) those without.
Single viscosity grade oils with the letter W are defined by maximum low
temperature cranking and pumping viscosities and a minimum kinematic viscosity
at 100C. Single grade oils without the letter W are based on a set of minimum
and maximum kinematic viscosities at 100C and a minimum high shear rate
viscosity at 150C. The shear rate will depend on the test method. Multigrade
grade oils are defined by both of these criteria....
The W is just a designation of one type of
testing vsvs.
another.
What is the viscosity of the
various weight oils? The definitions are as follows:
From SAE J300, viscosities at
212 F...
20, range - 5.6 to 9.2
30, 9.3 - 12.4
40, 12.5 - 16.2
50, 16.3 - 21.8
60, 21.9 - 26.1
By a modified analysis the
min. viscosity at 302 F...
20, 2.6
30, 2.9
40, 2.9 - 3.7
50, 3.7
60, 3.7
Note again that the
difference between the 20W and 60 weight oils at 302 F is only about 1 (one).
Whereas the difference in viscosity at 104 F is 120 units. The 20W has a
viscosity of 40 and the 60W a viscosity of 160. The difference at startup is
even higher, probably 250 or 300.
The American Petroleum
Institute, API, and Society of Automotive Engineers, SAE, have rated engine oil
performance over the years. We have seen the ratings go from SA, SB, SC, SD,
SE, SF, SG, SH, SJ, SL with SM to follow. SI and SK were eliminated as they are
used by other businesses. There are over 3 dozen tests that oil now must pass
in order to make the next higher rating. The tests are defined by the American
Society for Testing and Materials, ASTM. Some tests have progressed to a zero
tolerance level. For example there can be no sticking of any piston rings any
more. I will compare the SL rated oil to the previous SJ oil in a few
categories. For simplicity I will skip the units of measurement:
.......S J........S L......
.......30........20......maximum
cam plus lifter wear
........9.........7.8.....sludge
build up
........5.........8.9.....varnish
rating (more is better)
.......60.......45.......high
temperature deposits
.......17.......10.......high
temperature volatility
Other categories include:
Resistance to rust, resistance to foaming, resistance to oil consumption,
homogeneity and miscibility, flow reduction with varying amounts of absorbed
moisture, gelation index and others.
As one can see just going
from the previous SJ to the current SL rating is a significant improvement. I
cannot wait to get the upcoming SM oil into my cars.
Regarding cool whether gel
formation, a small except from SAE j300 1999:
4. Because engine pumping, cranking and
starting are all important at low temperatures the selection of an oil for
winter operation should consider both the viscosity required for oil flow as
well as cranking and starting, at the lowest expected ambient temperature.
Pumping viscosity is a
measure of an oils ability to flow...during the initial stages of operation.
Test in ASTM D 4684. ....samples are tested after a slow cool cycle. This cycle
has predicted as failures several SAE 10W-30 and 10W-40 oils which are known to
have suffered pumping failures in the field after short-term (2 days or less)
cooling. These field failures are believed to be the result of the oil forming
gel structures that result in excessive yield stress and viscosity of the
engine oil...
A.2.1...After preliminary
warming, the sample is subjected to a controlled temperature/time cycle over 5
1/2 to 7 days. The cycle reproduces ...instability or reversion which has
occurred during storage of oils in moderately cold cyclic conditions. Recent
work shows relevance to engine oil pumpability failure. Oils exhibiting pour
reversion have solids resulting from wax gel formation, at temperatures
significantly higher than their ASTM D 97 pour points.
Extracted, from ASTM D
4485-03 Standard Specification for Performance of Engine Oils, copyright ASTM
International, s
.
My point is that tests are
not just laboratory concoctions. They design tests to match real life
conditions.
I use 5W-20 Pennzoil mineral
based multigrade oil in my Expedition as it has many of the low temperature
characteristics of higher weight synthetic oils. My '04 manual states that the
SUV is delivered with a Ford semi-synthetic oil and although regular oil can be
used they recommend a semi or full synthetic oil. For the differential gear oil
they used 75W-140 in my ‘98 Expedition but now recommend 75W-90.
Please note that it makes no
difference what oil you are using. The 0W-20 Mobil 1 that is SL rated meets the
same criteria as that SL rated 10W-30 synthetic or mineral based Pennzoil. That
SJ or in particular that SH oil some people are looking for (from their older
automotive owners manual) is no where near as good as any SL oil of today.
Always use the most currently available, highest rated motor oil, even in the
oldest, most worn engine. You may require a thicker grade but just make sure it
is SL rated.
The SH rating was used in
oils starting 1993. The SJ rating started in 1997 while the SL became effective
in 2001 oils. According to ASTM D 4485, SL rated oils are superior to previous
oils and from:
X2.3.1 and 2: SL oil is for use in current and all earlier
passenger cars, sport utility vehicles, vans, and light trucks. This SL rated
oil can be used in engines requiring SJ and all earlier categories.
See: American Society for
Testing and Materials- www.astm.org
........Society of Automotive
Engineers- www.sae.org
........American Petroleum
Institute- www.api.org
Motor
Oil 108
Chapter
Eight. Odds and ends.
I have some stories that I collected.
First, my architect drives a big SUV. He was running with Mobil 1 brand 15W-50.
He changed it to Pennzoil Multigrade (mineral oil based, non-synthetic, cheap)
5W-20 at my suggestion. His gas mileage went from 10 to 13 MPG around town.
What really impressed him the most was the “robust” increase in “get up and
go.” He changed from a thick synthetic to a thin mineral oil. His venue is stop
and go city traffic in
The lower temperatures he was
seeing occurred because of reduced friction and internal drag and higher oil
flow.
One of the members of the
Ferrari Chat web site went from a 40 to a 30 weight oil in his Ferrari 355 for
racing in thanas it would have been at the previous
higher temperature. Cooler engines last longer. Fact: The higher the
temperature, the greater the wear, all other things being equal.
People say that their old car
manual says to use a 10W-40 so they would never think of using a 0W-40. Again,
both are the same viscosity at normal engine operating temperature. The 0W-40
just does not thicken as much after you turn off your engine. There are now
several cases when manuals for older cars have been updated to reflect this. My
550 Ferrari Maranello manual said to use 5W-40 yet the 575 manual says to use
the 0W-40. The engines are the same except the 575 has more BHP. It has better
acceleration and more top speed. The engines have the same tolerances.
All manufacturers I have seen
are specifying 0W-XX or 5W-XX oils now. Honda, Ferrari, Ford, Mercedes,
Porsche, and others specify a 0 or 5W-XX oil to mention a few. These are
appropriate for all engines of all ages of all levels of wear. This second
number is the only thing that may change with an older, lose or worn engine.
This can only be determined by experimentation. If you are using XW-50, go to a
0W-40. If your pressures are still too high go to a 0W-30 and so on.
When I took delivery of my
575 Maranello I drove for 500 miles then changed the oil to 0W-30 Mobil 1.
There were no changes in operating pressure or temperature. Starting the engine
seemed faster though. I called up FNA and was told that all new Ferrari cars
are delivered with 5W-30 Shell Helix Ultra. That is when I decided to try the
0W-20 Mobil 1. I could even go to a 10 weight oil as my pressures are still excessive
while driving around town. I do not drive on the track.
What about the break in
period? For one thing you could just follow the car’s manual and gradually
break your engine in. Some cars like Ferrari and Lamborghini run engines and
the cars for a period of time before you even take delivery. They often run up
to full power. Some representatives at least from Ferrari hinted that the
traditional break in period was not really needed, at least in their car.
Most people who buy high
powered cars that I have experienced will just get in there cars and step on
the gas fully. They do not wait for the oil to warm up. Personally I would not
mind running full BHP for short bursts during the break in period but I always
fully warm up the engine first.
Older engines may in fact
benefit from thinner oil use. Over time permanent deposits of carbon and sludge
build up in the engine oil ways. It is like a clogging of arteries in humans.
We are now all on blood thinners. This is an area I specifically studied while
a general surgeon resident at
Thinner oils, and
specifically synthetic products are better. Some people say their engines were
“designed” to run on mineral based lubricates. I have not seen anything to
support this theory. The synthetic of the same viscosity as the mineral oil you
are now using will be an improvement. If you go from a mineral to an even
thinner synthetic you may be better off still. The pressures go up in many
older engines because of this “clogging” of the arteries. Most think this is
good but it is really a lessening of flow and therefore accelerates engine wear
even further.
For those engines with
excessive varnish and carbon buildup the engine oil additives of the detergent
type may be of benefit. On the other hand you could just use a thin synthetic
oil and change it every 200 miles for a while and end up with an even cleaner
engine. With everything working properly you may actually need a thicker oil if
that engine is overly worn. The thicker oil would be a disaster however, if the
arteries were narrowed from deposits.
Remember, the only difference
between a 0W-40 and a 10W-40 is that the 0W-40 thickens less after you turn off
your engine. It is still too thick in the morning at startup but not as thick
as the 10W-40. Yet, they are still too thick to use until they both warm up to
operating temperature at which point they have the save viscosity, around 13 to
14. Remember that the 0W-30, 10W-30 and straight 30 weight oils all have a
viscosity of around 10 at normal engine operating temperatures.
There is one more thing. A 20
weight oil is not half as thick as a 40 weight oil. The real scale is more like
the oils having an absolute thickness of 108 and 114. Now it can be seen that
the 40 weight oil is only around 10 percent thicker than the 20 weight oil. The
difference is not that much at operation but at startup the difference is
significant. Pressure / flow dynamics go along with this 10 percent figure. A
30 weight oil should be thought of as having an absolute viscosity of 110 and a
50 weight oil has an absolute viscosity of 120. I am talking about operating
temperatures.
I thought everyone knew that
90 percent of engine wear occurs during the startup period because oil is just
too thick. Some think it is good to have a thicker oil for startup since the
parts shrink when cold and would otherwise “rattle.” Sure, your piston diameter
will shrink on cooling but so will the diameter of your bore. The net result is
about the same clearance hot and cold. This is not true for your valves. They
lengthen when extremely hot. In the Murcielago they use shims instead of self
adjusting valve tappets. You need to put a millimeter of clearance there so
that after expansion the valve will not be held partly open when it is supposed
to be closed.
It it
were true that thicker oils were needed at startup then the manufacturers would
not be requesting oils that thicken less on cooling. They would just specify
that one should use a straight 30 or 40 weight oil. Instead, over time, they
are specifying thinner and thinner oils.
The manufacturers know what
parts shrink or expand and the clearance changes that result. You do not have
to worry about this. If it was that easy to design engines we would all be
making them.
I would like to go back to
the worry that oil falls off the parts when a car is stored or sees long
periods of inactivity. For the first oil change in my 575 Maranello I drained
the Shell and put in 0W-30 Mobil 1. This was at 775 miles on the odometer. I
drove the car home from work, put it on the lift and drained the transaxle and
engine oils. I also opened and drained the oil cooler and took off every line
that is in the oil system. I wanted to get every speck of the Shell oil out of
there. For optimal results you are not supposed to mix synthetic oils of
different brands.
The system takes 12 quarts
with a “normal” oil change but took 15 quarts for this change. It all took
about an hour. I then started the engine to check for leaks. The multitude of
mechanical engine noises that followed nearly broke my eardrums for about 10
long seconds. Then it was suddenly very quiet. You could hear a pin drop. There
was certainly the most possible amount of surface oil on all the internal parts
as the engine was only off for an hour. But it was not until the oil circuit
primed, filled then sent flow into all the parts that any lubrication was
occurring. Hence all oil filters that are manufacturer certified have back flow
limiters to keep the oil filter full even with the engine off.
Here is an interesting tidbit
of information. A 75W-90 gear oil has the same viscosity as a 10W-40 engine oil
at 212 and 302 F. Once again, those numbers on that oil can are misleading and
certainly add to the confusion I see among automotive enthusiasts.
aehaas
Motor
Oil 109
Chapter
nine. Let’s start over.
We have seen that 0W-30,
5W-30, 10W-30 and straight 30
weight oils all have the exact same viscosity at 212 and 302 F. What about
startup viscosities? Do 0W-20, 0W-30 ,
and 0W-40 all have the same viscosity at
a 75 F startup. The answer is no. The SAE J300 standard allows for this
discrepancy. Here are some examples:
..Viscosity at 75 F startup..
...0W-20.....0W-30.....0W-40
.....40............50...........60
The numbers are not exact but
they show clearly that the ”0” represents different startup viscosities. This
is unlike the 0W-30, 5W-30, 10W-30 and straight 30 weight oils that all have
the exact same viscosity in a hot engine = 10 cS.
I would like to comment on
the following statements made by a knowledgeable automotive enthusiast:
“Pressure and flow are tied
together with viscosity, but none have anything to do with lubrication.
Lubrication is a property of the fluid, not the force. The oil pump would pump
water just as well, but it would offer no real lubrication. If we double the
pressure, we double the flow. If you decrease the viscosity to a lighter oil,
you increase flow at a loss of pressure. High flow helps to carry away more
heat. High pressure helps to keep metal parts like the bearings out of contact
with each other (scuffing).”
I give you the following
example to help visualize what is happening. This assumes the oil has no
internal resistance. In actuality doubling the pressure will not double the
flow but will be slightly less. And thicker oils have more resistance than
thinner oils for all situations. But simplified we get the following:
For a 30 wt oil at operating
temperature:
RPM....Pressure..Flow
1,000......20 PSI....1
2,000......40 PSI....2
4,000......80 PSI....4
8,000... 160 PSI....8 The maximum flow because of the oil pop off
valve at 90 PSI will be 5
For a 30 wt oil at operating
temperature
and a higher output oil pump:
RPM....Pressure..Flow
1,000......30 PSI....1.5
2,000......60 PSI....3
4,000....120 PSI....6 The maximum flow because of the oil pop off
valve at 90 PSI will be 5
8,000... 240 PSI....12
If we stick with the same
weight oil and increase the oil pump output we will increase the pressure and
the oil flow too. If we double the oil pump output we will double the pressure
and we will double the oil flow (in an ideal system).
RPM....Pressure..Flow
1,000......40 PSI....2
2,000......80 PSI....4
4,000....160 PSI....8 The maximum flow because of the oil pop off
valve at 90 PSI will be 5
8,000... 320 PSI....16
Let us compare a 40 wt oil at
operating temperature:
The oil is thicker, has more
internal resistance and therefore requires more pressure to get the same flow.
RPM....Pressure..Flow
1,000......30 PSI....1
2,000......60 PSI....2
4,000....120 PSI....4 The maximum flow because of the oil pop off
valve at 90 PSI will be 3
8,000....240 PSI....8
For a 40 wt oil at operating
temperature
and a higher output oil pump:
RPM....Pressure..Flow
1,000......45 PSI....1.5
2,000......90 PSI....3 The maximum flow because of the oil pop off
valve at 90 PSI will be 3
4,000....180 PSI....6
8,000... 360 PSI....12
For a 40 wt oil at operating
temperature
with the original pressures:
RPM....Pressure..Flow
1,000......20 PSI....0.5
2,000......40 PSI....1
4,000......80 PSI....2
8,000... 160 PSI....4 The maximum flow because of the oil pop off
valve at 90 PSI will be 3
Increasing the pressure while
using the same oil will increase the oil flow but increasing the pressure by
increasing the oil thickness will result in less flow. It takes more pressure
to move a thicker oil. When you go to a thicker oil the pressure goes up
because of the increased resistance, and therefore reduction of flow.
There is more to these graphs
but I will contiuecontinue
with the next chapter.
Furthermore pressure does not
equal lubrication. Let us look at a single closed “lifetime lubricated”
bearing. We could hook up a system to pressurize the bearing. This can actually
be done. We could have the oil at ambient pressure. We could then double,
triple, quadruple the pressure of the oil. The oil is non-compressible.
Regardless of the pressure we would have the exact same lubrication, that of
the ambient pressure lubrication.
The physics of lubrication as
I said earlier show a 1:1 relationship of flow to separation pressure.
Lubrication itself is pressure independent. I will not go into the mathematical
equations for this.
Even water can be used as a
lubricant. This is partly because of its high surface tension. It is used in
many medical devices and other systems that are under or exposed to water. It
is just that water rusts metal parts making this unsuitable for automotive
engines. It actually has a higher specific heat than oil. It can therefore
carry away more heat than oil from bearing surfaces. In this respect water is a
better lubricant than oil.
aehaas
Motor Oil 201
Chapter 10, The graduate.
I am going to bring up the
constant flow pump concept. First, it goes back to the principal that doubling
the pressure of the same weight oil does not exactly double the flow but it is
close. Also doubling the RPM for the same reason does not exactly double the
flow but again it is close.
This shows the problem best:
(A) For a 30 wt oil at
operating temperature:
RPM....Pressure..Flow
1,000......20 PSI....1
2,000......40 PSI....2
4,000......80 PSI....4
8,000... 160 PSI....8 The maximum flow because of the oil pop off
valve at 90 PSI will be 5
(B) For a 30 wt oil at
operating temperature
and a higher output oil pump:
RPM....Pressure..Flow
1,000......30 PSI....1.5
2,000......60 PSI....3
4,000....120 PSI....6 The maximum flow because of the oil pop off
valve at 90 PSI will be 5
8,000... 240 PSI....12
If we stick with the same
weight oil and increase the oil pump output we will increase the pressure and
the oil flow too. If we double the oil pump output we will double the pressure
and we will double the oil flow.
(C) For a 40 wt oil at
operating temperature:
The oil is thicker, has more
internal resistance and therefore requires more pressure to get the same flow.
Compare this with (A):
RPM....Pressure..Flow
1,000......30 PSI....1
2,000......60 PSI....2
4,000....120 PSI....4 The maximum flow because of the oil pop off
valve at 90 PSI will be 3
8,000....240 PSI....8
(D) For a 40 wt oil at
operating temperature
and a higher output oil pump:
RPM....Pressure..Flow
1,000......45 PSI....1.5
2,000......90 PSI....3 The maximum flow because of the oil pop off
valve at 90 PSI will be 3
4,000....180 PSI....6
8,000... 360 PSI....12
The situations (A) and (C)
are close to real life, assuming no loss in the system. This is what happens
when you change the 30 weight oil to a 40 weight oil in your car:
(A) For a 30 wt oil at
operating temperature:
RPM....Pressure..Flow
1,000......20 PSI....1
2,000......40 PSI....2
4,000......80 PSI....4
8,000... 160 PSI....8 The maximum flow because of the oil pop off
valve at 90 PSI will be 5
(C) For a 40 wt oil at
operating temperature:
The oil is thicker, has more
internal resistance and therefore requires more pressure to get the same flow.
RPM....Pressure..Flow
1,000......30 PSI....1
2,000......60 PSI....2
4,000....120 PSI....4 The maximum flow because of the oil pop off
valve at 90 PSI will be 3
8,000....240 PSI....8
At 6,000 RPM the maximum rate
of flow has been reached with the thinner oil (A). When you go to 7, 8 or 9,000
RPM you do not get any more flow. You only get a maximum rate of 5. The
internal forces on the bearings increase but there is no additional flow of
oil.
With the thicker oil you
reach maximum flow at 3,000 RPM (C). Worse yet is that the maximum flow is now
only 3. As we increase RPM to 4, 5, 6, 7, 8, 9,000 RPM we get no additional
pressure and no additional flow, no increase in lubrication.
Next let us look at a 20
weight oil at operating temperature. We get the same flow out of our constant
volume pump but the thinner oil requires less pressure to move through the
system. This even goes along with the rule that we should use an oil that gives
us 10 PSI per 1,000 RPM:
(D) RPM....Pressure..Flow
1,000......10 PSI....1
2,000......20 PSI....2
4,000......40 PSI....4
8,000.. ...80 PSI....8
The maximum flow rate has not
been reached. If the engine went to 9,000 RPM then the flow would be 9 at 90
PSI, our maximum pressure at pop off. The engine now has 3 times the flow rate
as with the 40 weight oil at full RPM. The nozzles at the bottom of each
cylinder are spraying 3 times the amount of oil lubricating and cooling this
section. Everything runs cooler and the separation forces in the bearings are 3
times higher.
For engines that redline at
5,000 RPM they usually pop off the oil pressure at 50 to 60 PSI. For engines
that go to 8-9,000 RPM the pressures max out at 90-100 PSI. You can now see
that you can only get the maximum flow rate if you follow the 10 PSI / 1,000 RPM
rule.
The winner: 0W-20 weight oil
for my Maranello. I said earlier that I could use a 10 weight oil. I actually
only run with 185 F oil temperature around town and the pressures are similar
to the 40 weight oil example in (C) above. This is why I also said that in the
racetrack condition, with hotter, thinner (0W-20) oil I may actually get the
optimal results as in (D) above.
Now let us go back to the
Ferrari recommended parameters in my 575 Maranello manual. It calls for 75 PSI
at 6,000 RPM. The pop off pressure has not been reached. As we now increase the
RPM we still get an increase in flow rate. This is what we need and this is
exactly what they are recommending. We get our maximum flow at the maximum
system pressure, at about the maximum engine RPM of 7,700. There is no
bypassing of the oil. All oil pumped goes through the system. There is no
wasted BHP pumping oil past the bypass valve back to the oil tank. It is the
perfect system.
Finally I will compare a
single, 30 weight oil, at normal (212 F) and at racetrack (302 F) temperatures:
(A) For a 30 wt oil at normal
(212 F) operating temperature:
RPM....Pressure..Flow
1,000......20 PSI....1
2,000......40 PSI....2
4,000......80 PSI....4
8,000... 160 PSI....8 The maximum flow because of the oil pop off
valve at 90 PSI will be 5
(E) For a 30 wt oil at
elevated (302 F) operating temperature. The oil is thinner at 302 F. It
requires less pressure to get the same flow:
RPM....Pressure..Flow
1,000......10 PSI....1
2,000......20 PSI....2
4,000......40 PSI....4
8,000......80 PSI....8 The maximum flow because of the oil pop off
valve at 90 PSI will be 9
The hotter (302 F) 30 weight
oil is thinner than the cooler (212 F) 30 weight oil. It has the same flow rate
in the constant volume oil pump but at a lower pressure than the oil at normal
operating temperature. This allows for a doubling of the flow rate at peak RPM.
The thinning of oil at higher temperatures is a benefit. You get more flow,
more cooling and more lubrication.
The 30 weight oil at 302 F has
the exact same flow rate and pressures as the 20 weight oil at 212 F. See (D)
above. Therefore, use the 20 weight for around town driving and the 30 weight
on the hot track. You get maximum flow at each situation.
For YOUR engine, substitute
the actual flow at 1,000 RPM. If your engine puts out 1.5 liters/min. at 1,000
RPM it would put out 3 liters/min. at
2,000 RPM and 6 liters/min. at 4,000 RPM and so on. The maximum flow in
(A) would be 7.5 liters/min. In situations (D) and (E) you would get a maximum
of 13.5 liters/min.
Conclusions:
The reason that multigrade
oils were developed in the first place was to address the problem of oil
thickening after engine shutdown. Over the years we have been able to reduce
the amount of thickening that occurs. Never-the-less there is no oil that does
not thicken after you turn your engine off. This is why we have to warm up our
engines before revving them up. Engine designers always pick the recommended
oil based on a hot engine and hot oil. There is no issue with oil thinning as
they are both matched when hot. The problem is oil thickening when the engine
cools.
Cold engine showing very high
pressures because of the thickened oil at startup:
For a 40 wt oil at 75 F at
startup:
The oil is thicker, has more
internal resistance and therefore requires more pressure to get the same flow.
RPM....Pressure..Flow
1,000......60 PSI....1
2,000....120 PSI....2 The maximum flow because of the oil pop off
valve at 90 PSI will be 1.5
4,000....240 PSI....4
8,000....480 PSI....8
At 1,500 RPM you reach the
maximum oil flow rate and if you run to 8,000 RPM it is the same rate. The flow
cannot increase and it is insufficient. This is why we must wait until our oil
temperature comes up to 212 F or higher. The maximum flow rate in this case
will then double, up to 3. To get even more flow in our test engine you need to
use a lower viscosity grade.
If you have absorbed and
digested the information here you should be able to pick out the proper
operating oil weight for your car, be it a 30, 40, 50 or even 20 weight oil. I
have always used oils that were a grade thinner than recommended even though
many use a grade thicker than recommended. I showed evidence that the starting
grade should always be 0 or 5 (0W-XX or 5W-XX for thicker oils). If you want
the best protection and highest output from your motor use a synthetic based
oil. The actual brand is not as critical as the viscosity. The rating must be
SL or the upcoming SM rating. Change
your oil every 3 - 5,000 miles and at least every spring.
Final examination to follow
later.
THE END
Motor
Oil Midterm Examination
Answer questions without
looking back. This is a closed book exam. Base your answers on the information
provided in these past chapters.
1- At normal operating
temperature, 212 F, a straight 30 weight oil has a viscosity of how many
centiStokes?
A- 3
B- 6
C- 10
D- 20
E- 30
2- While racing at 95 F,
mid-summer in
A- 0W-40
B- 5W-40
C- 10W-40
D- Straight 40 weight
E- They are all exactly the
same
3- While starting up your car
at 75 F, mid-winter in Florida, what is the approximate viscosity of a straight
10 (ten) weight motor oil?
A- 3 cS
B- 6 cS
C- 10 cS
D- 20 cS
E- 30 cS or higher
4- The biggest problem with
mineral based motor oils with long tern use is:
A- Thinning
B- Thickening
C- Loss of VI (viscosity
index) improvers
D- Both A and C
E- None of the above is
correct
5- Which of the following
mineral based motor oils are still too thick at a 75 F startup
temperature?
A- 20 weight
B- 10 weight
C- 5 weight
D- All of the above
E- None are too thick
Answers to the Oil Midterm
Exam
I feel these were all
difficult questions. You would be doing well to get 3 correct.
1- At normal operating
temperature, 212 F, a straight 30 weight oil has a viscosity of how many
centiStokes?
A- 3
B- 6
C- 10
D- 20
E- 30
The correct answer is C- 10
cS.
2- While racing at 95 F,
mid-summer in
A- 0W-40
B- 5W-40
C- 10W-40
D- Straight 40 weight
E- They are all exactly the
same
The correct answer is E- They
are all exactly the same.
3- While starting up your car
at 75 F, mid-winter in Florida, what is the approximate viscosity of a straight
10 (ten) weight motor oil?
A- 3 cS
B- 6 cS
C- 10 cS
D- 20 cS
E- 30 cS or higher
The correct answer is E- 30
cS or higher.
4- The biggest problem with
mineral based motor oils with long tern use is:
A- Thinning
B- Thickening
C- Loss of VI (viscosity
index) improvers
D- Both A and C
E- None of the above is
correct
The correct answer is B-
Thickening
5- Which of the following
mineral based motor oils are still too thick at a 75 F startup
temperature?
A- 20 weight
B- 10 weight
C- 5 weight
D- All of the above
E- None are too thick
The correct answer is D- All
of the above
Motor
Oil Final Examination
Answer questions without
looking back. This is a closed book exam. Base your answers on the information
provided in these past chapters.
1- While starting up your car
at 75 F, mid-winter in
A- 0W-20
B- 0W-30
C- 0W-40
D- 0W-50
E- They are all exactly the
same
2- While vacationing in
A- 10 cS
B- 20 cS
C- 30 cS
D- 100 cS
E- 400 cS
3- While vacationing in
A- 1
B- 10
C- 20
D- 40
E- 400
4- Assume there are no losses
in the system and your oil pump is truly volume based. Also assume there is no
cut off pressure valve and you are using a 40 weight motor oil. If at 1,000 RPM
your pressure is 30 and your pump output is 1 (one), what will the pressure and
output be at redline, 8,000 RPM?
A- 240 PSI, flow = 8
B- 180 PSI, flow = 8
C- 240 PSI, flow = 4
D- 180 PSI, flow = 4
E- 120 PSI, flow = 8
5- Water can be used as a
lubricant.
A- True
B- False
6- If you increase the
pressure in a bearing, all other things being constant, the force of separation
between the parts increases.
A- True
B- False
7- The best weight oil for
racing any Ferrari or Lamborghini is a
40 weight multigrade synthetic oil like Mobil One 0W-40.
A- True
B- False
8- For my Maranello 575 the
0W-20 weight Mobil 1 oil is actually too thick for my driving conditions.
A- True
B- False
9- The major problem with
engine oil is that it thins with increasing temperature.
A- True
B- False
10- Your 1993 sports car
manual states to use an API / SAE SH rated 10W-40 mineral based motor oil. Your
engine has only 1,550 miles on the odometer. On your next oil change it would
be better to use a SM rated 0W-40 synthetic oil.
A- True
B- False
11- According to SAE J300 a
30 weight oil has a viscosity of between 9.3 and 12.4 centiStokes at operating
temperature (212 F).
A- True
B- False
12- In my list of recommended
oils what did I list as the best mineral based motor oil in the 50 weight
class?
A- Pennzoil multigrade 20W-50
B- Castrol GTX 15W-50
C- Red Line 10W-50
D- Valvoline Durablend 0W-50
E- No oil was recommended
13- You are running 5W-40
Shell Helix Ultra fully synthetic motor oil in your Mercedes Benz. You are in a
K-Mart shopping center and checked your oil and it is 1 1/2 quarts low. You
will need to add one can of oil. Which of the following is the best choice.
A- Mobil 1 - 0W-40
B- Pennzoil Synthetic 5W-40
C- Red Line Synthetic 5W-40
D- Castrol Syntec 0W-30
E- Shell mineral based 10W-40
14- Motor oils that are
labeled “for racing only” should not be used for everyday driving because:
A- They do not have
detergents
B- They may have harmful
levels of some additives
C- They are generally
unrated, there is no SJ, SL or SM approval
D- You would have to take
your engine apart and clean it periodically
E- All of the above
15- ASTM stands for:
A- Automotive Standards and
Test Methods
B- Automotive Society for Tooling
and Machining
C- American Society for
Testing and Materials
D- American Standards Trade
and Manufacturing
E- Society for American
Standard Testing Methods
16- If your engine is running
too hot at higher RPM one thing you can try to bring the temperature down is to
use a thinner oil.
A- True
B- False
17- Oil with a startup
thickness of 100 (at 75 F) that becomes the appropriate thickness of 10 when
fully warmed up (212 F) is called a 10W-30 weight motor oil.
A- True
B- False
18- A main advantage that the
synthetic has over the mineral based oil of the same grade is the ability to
lubricate better at startup.
A- True
B- False
20- I am (single best
answer):
A- Surgeon
B- Biochemist
C- ‘Halfass mechanic
D- Absurdly interested in
motor oils
E- All of the above
Answers below:
Answers to the Oil Final Exam
I feel these were all very
difficult questions. You would be doing well to get 10 correct.
1- While starting up your car
at 75 F, mid-winter in
A- 0W-20
B- 0W-30
C- 0W-40
D- 0W-50
E- They are all exactly the
same
The correct answer is A- 0W-20.
2- While vacationing in
A- 10 cS
B- 20 cS
C- 30 cS
D- 100 cS
E- 400 cS
The correct answer is D- 100
cS
3- While vacationing in
A- 1
B- 10
C- 20
D- 40
E- 400
The correct answer is A- 1
4- Assume there are no losses
in the system and your oil pump is truly volume based. Also assume there is no
cut off pressure valve and you are using a 40 weight motor oil. If at 1,000 RPM
your pressure is 30 and your pump output is 1 (one), what will the pressure and
output be at redline, 8,000 RPM?
A- 240 PSI, flow = 8
B- 180 PSI, flow = 8
C- 240 PSI, flow = 4
D- 180 PSI, flow = 4
E- 120 PSI, flow = 8
The correct answer is A- 240 PSI, flow = 8
5- Water can be used as a
lubricant.
A- True
B- False
The correct answer is A- True
6- If you increase the
pressure in a bearing, all other things being constant, the force of separation
between the parts increases.
A- True
B- False
The correct answer is B- False
7- The best weight oil for
racing any Ferrari or Lamborghini is a
40 weight multigrade synthetic oil like Mobil One 0W-40.
A- True
B- False
The correct answer is B- False. It can best be determined by
driving the car with one type of oil and see what happens.
8- For my Maranello 575 the
0W-20 weight Mobil 1 oil is actually too thick for my driving conditions.
A- True
B- False
The correct answer is A- True
9- The major problem with
engine oil is that it thins with increasing temperature.
A- True
B- False
The correct answer is B- False. The problem is thickening when the
engine is turned off. With long term use the problem is also thickening.
10- Your 1993 sports car
manual states to use an API / SAE SH rated 10W-40 mineral based motor oil. Your
engine has only 4,550 miles on the odometer. On your next oil change it would
be better to use a SM rated 0W-40 synthetic oil.
A- True
B- False
The correct answer is A- True
11- According to SAE J300 a
0W-30 and a straight 30 weight oil must have a viscosity of between 9.3 and
12.4 centiStokes at operating temperature (212 F).
A- True
B- False
The correct answer is A- True
12- In my list of recommended
oils what did I list as the best mineral based motor oil in the 50 weight
class?
A- Pennzoil multigrade 20W-50
B- Castrol GTX 20W-50
C- Red Line 15W-50
D- Valvoline Durablend 20W-50
E- No oil was recommended
The correct answer is E- No oil was recommended. They all are too
thick at startup for daily use.
13- You are running 5W-40 Shell
Helix Ultra fully synthetic motor oil in your Mercedes Benz. You are in a
K-Mart shopping center and checked your oil and it is 1 1/2 quarts low. You
will need to add one can of oil now. Which of the following is the best choice.
A- Mobil 1 - 0W-40
B- Pennzoil Synthetic 5W-40
C- Red Line Synthetic 5W-40
D- Castrol Syntec 0W-30
E- Shell mineral based 10W-40
The correct answer is E- Shell mineral based 10W-40. You can mix
any SM rated oil in there but this is my first choice based on my research.
14- Motor oils that are
labeled “for racing only” should not be used for everyday driving because:
A- They do not have
detergents
B- They may have harmful
levels of some additives
C- They are generally
unrated, there is no SJ, SL or SM approval
D- You would have to take
your engine apart and clean it periodically
E- All of the above
The correct answer is E- All of the above
15- ASTM stands for:
A- Automotive Standards and
Test Methods
B- Automotive Society for
Tooling and Machining
C- American Society for
Testing and Materials
D- American Standards Trade
and Manufacturing
E- Society for American
Standard Testing Methods
The correct answer is C- American Society for Testing and Materials
16- If your engine is running
too hot at higher RPM one thing you can try to bring the temperature down is to
use a thinner oil.
A- True
B- False
The correct answer is A- True
17- Oil with a startup
thickness of 100 (at 75 F) that becomes the appropriate thickness of 10 when
fully warmed up (212 F) is called a 10W-30 weight motor oil.
A- True
B- False
The correct answer is A- True
18- A main advantage that the
synthetic has over the mineral based oil of the same grade is the ability to
lubricate better at startup.
A- True
B- False
The correct answer is A- True
19- In ASTM D 4485 3.1.4:
Engine oil is defined as - - “a liquid that reduces friction and wear between
moving parts within an engine, and also serves as a coolant.”
A- True
B- False
The correct answer is A- True
20- I am (single best
answer):
A- Surgeon
B- Biochemist
C- ‘Halfass mechanic
D- Absurdly interested in
motor oils
E- All of the above
The correct answer is E- All
of the above
The talk:
Hello Dr. Haas,
Allow me to start by offering
my thanks for taking the time to produce such an easy to follow and informative
article on engine oil. Using your information I changed from 20W 50 dino oil in
my 1977 308 GTB to Mobil One 0W 40. The results have been fantastic especially
at start up where all previous noises are gone.
Robert,
Mr. Haas, thank you. I have
raced motorcycles and cars for years. I will freely admit to subscribing to
more than 1 of the “myths” detailed in your wonderful dissertation. If it is
clear enough for an old dog to understand and change his ways, it’s a well
written explanation. I have read every chapter end to end. Again, thank you.
I've been trying to figure
out the best oil for my 328 for the several months that I've owned it. I've
read all the posts, checked the manual, changed oil with different weights a
couple of times, monitored pressure and temperatures, fussed over correct
levels etc. Now, with a sense of relief, I can settle with a decision with some
confidence. It will be Mobil One 0w40. I tried 15/50 and the pressure was a bit
high according to the manual, and I've tried 5/30 and it was a bit low-though
both in the ballpark.