Porsche 928 S4 Service
John Pirtle, February 2, 2001
http://members.rennlist.com/pirtle
Cooling System
The 928 cooling system is unique not only because it is Porsche's first,
but its design is such that cold spots are better eliminated during warm-up. This
design mandates that the engine NEVER be run without a thermostat.
The temperature gauge is reasonably accurate and typical driving will place
the gauge about midway. Very warm days may cause the engine to run warmer than
usual. Spirited driving will also quickly raise the coolant temperature. This
is normal behavior although the needle should NOT rise above the final mark into
the red zone. Never operate the aluminum engine in an overheated state.
Some causes for overheating include inoperable radiator fans and
non-functional cooling flaps on the S4 model. The radiator fans should cycle
on/off. They should also come on any time the A/C button is pushed in.
The cooling flaps should always fully open when the engine is turned off.
If not, check the fuse. Also remove the rubber cap over the manual flap
adjustment knob in the middle of the flaps. Turning the knob will open/close
the flaps. Many specialists recommend manually opening the flaps fully, and
removing the fuse to disable the system which primarily is designed to assist
air flow and achieve a 0.34 drag coefficient (0.36cd with the flaps open).
Most specialists recommend yearly coolant changes. Only use aluminum-friendly
coolant. Distilled water is highly recommended so as not to introduce various
minerals into the aluminum engine.
No special tools are needed. The supply list is:
- Texaco Havoline Dex-Cool coolant - 2 gallons
- Distilled water - 2 gallons
- Redline Water Wetter (often recommended)
- 75ºC thermostat and gasket
This is a good time to consider replacing both upper and lower radiator
hoses, the heater hoses, the coolant reservoir hose, the heater valve, and
the radiator cap.
- Start with a COLD engine.
- Loosen coolant reservoir cap.
- Remove engine belly pans (if you have them!).
- Clean any debris away from the radiator. While you're in there,
check for the E-clip on the headlight actuator arm (so that it does
not come loose and punch your expensive radiator).
- Loosen the radiator drain cock (flathead screwdriver) and drain
the radiator. You will catch about 2½ gallons.
- Remove the left and right side engine block freeze plugs (13mm) and
drain block. Be careful, these can strip easily. You should catch about
1½ gallons.
- Remove the air cleaner intake hoses.
- Remove the upper radiator hose at the radiator.
- Remove the lower radiator hose at the thermostat housing.
- Remove the thermostat housing.
- Remove the thermostat noting its installed position.
- Clean the old gasket material away.
- Install the new thermostat fitting the smaller end properly inside the housing.
- Locate the gasket and bolt the housing to the water manifold.
- Replace and snug radiator drain cock.
- Replace the two engine block freeze plugs. Be careful with aluminum !
- Attach the lower radiator hose to the radiator.
- Attach the upper radiator hose to the water manifold.
- Fill the engine block with a coolant mix through the upper radiator
hose and then connect the hose to the radiator. The mix should be approximately
50/50% aluminum-friendly coolant and distilled water (adjust the ratio to your
climate).
- Fill the radiator through the lower radiator hose and then connect
the hose to the thermostat housing.
- Fill the coolant reservoir. (Leave the cap off.)
- Start the engine and set heater to full HOT and fan on maximum.
- Watch for leaks and listen for bad noises.
- When coolant reaches operating temperature the thermostat will open
and the lower radiator hose will begin to warm. At that point periodically
squeeze the lower radiator hose to help move air out of the system.
- After the engine has fully warmed, shut it off.
- Check radiator hose clamps.
- Watch for leaks.
- Top off coolant in the reservoir and tighten the cap.
- Go for a drive, listening for odd noises and checking for leaks.
- Check accessory belt tension.
- After engine cools check the coolant reservoir level.
- Replace engine belly pans.
- Wash car. :)
- Over the next few days check for leaks and the coolant reservoir level.
Water manifold
The water manifold brings together the upper and lower radiator hoses,
the thermostat, coolant expansion tank hose, coolant temp sensor, and
fuel injection temp sensor. By removing the water manifold access beneath
the front of the intake can be gained for replacing hoses, etc.
This is a good time to replace the thermostat. The water manifold
itself has a large O-ring at the bottom, and two eccentrically shaped
o-rings at each end.
