|Oil Temperature Tests|
|When I drive the car on the track, I have oil temperature problems...it
gets quite hot during a typical 25-minute session. I decided to investigate
this problem and see if I could devise a solution. Note that I had already
added an external oil cooler, with air pickup under the left, rear suspension.
Before I started, I bought a good 4-channel k-type thermocouple meter (an
Omega HH501DK). This was an essential tool.
I positioned thermocouples in various places on and around the engine and drove the car to get temperature readings. I decided on a standard 30-minute, 28-mile roundtrip for these tests. It's a slightly hilly section of rural farm-to-market road that is lightly traveled. I drove at a constant 70 MPH for the tests. I found several interesting things:
1. The air at the back of the engine compartment is much hotter than the air at the front...about 15 degrees F higher! There are probably several reasons: 1) the transmission, exhaust, and muffler are behind the engine, plus, all the hot cooling air goes to the rear...all this heat causes the sheet metal at the rear of the engine to be quite hot and it heats the air inside the engine bay; 2) the engine mounted fan keeps air moving across the front of the engine which keeps the air at the front cooler. Since the inlet to the air cleaner is at the rear, the engine is drawing in hot air. Even the air at the front of the engine compartment is about 15 degrees F higher than ambient.
2. When I started, my baseline was an oil temperature rise of 142 degrees F above ambient. This seemed to be rather constant, regardless of the ambient...over the short test range of about 75 to 105 degrees F. Thus, when the ambient was 100 degrees F, the oil temperature was 242 degrees F. Note that this was not really pushing the engine as on the track...it was just a lazy drive in the country, at legal speeds!
3. Removing or opening the engine lid, resulted in a 4 degree F improvement. I never tested removing the rain tray...it had been removed years earlier. I'm sure it helps out a degree or two, but I don't have any data...sorry.
4. Years earlier, I had substituted short air deflectors...these are the soft plastic thingies that are attached to the body just in front of the engine. These disrupt the air flow, making it turbulent and helping extract heat from the engine. I replaced these with original deflectors and noticed a 7 degree F improvement. These are quite important!
5. Moving the air pickup for the external oil cooler from under the left, rear suspension to a NACA duct in the left rocker panel improved the oil temperature 5 degrees F. I believe that the problem with the original location was that some hot cooling air from the engine was spilling over and entering the external oil cooler air inlet...the air flowing across the rocker panel was cooler. But I suspected that this location for the NACA duct might be less than optimal. They typically need to be mounted in relatively uncluttered panels and not near an edge.
6. So I moved the air pickup for the external oil cooler from the NACA duct to a 7 square inch scoop mounted outboard of the left rocker panel. This reduced the oil temperature an additional 7 degrees from the NACA duct setup.
7. I added a scoop to the right sail panel that ducted air to the engine compartment. This improved the oil temperature 4 degrees F.
8. I extended the air inlet for the engine, by adding a duct that picked up air from the right sail panel scoop. This improved the oil temperature an additional 4 degrees F.
9. I changed the ignition timing from the nominal 27 degrees BTDC to 35 degrees BTDC. This decreased the oil temperature 1 degree F.
In summary, by adding a right-side air scoop and sending part of this air directly to the engine air cleaner, moving the air inlet for the external oil cooler to a left-side scoop on the rocker panel, using the stock under-car air deflectors, and increasing the ignition timing 8 degrees, I reduced the oil temperature 30 degrees F.
|Here are pictures of the right-side scoop and the duct to the air cleaner. The scoop uses 3 existing holes to mount to the car (no new holes). The flat black paint on the scoop really doesn't look quite that gray in real life. I remove the air duct in the winter, to help the engine heat up quicker.|
|Here are pictures of the scoop mounted in the left rocker panel. In the first picture, you can see where the NACA duct was previously mounted. Yes, that's a soup can! It fits the 3" flex-duct perfectly!|