As an addition to my previous oil thread, we have been trying to diagnose an oil pressure issue that we had with the car at a race this past weekend. It is a really odd issue and I have some ideas, but I wanted to throw this out to you guys who have a lot more experience with piston engines (I am a long time rotary guy). What is interesting is that the previous owner of the car was at the race and he confirmed the oil temps always ran between 240 and 250 degrees and that he saw the same issues when he ran the car.

When I fire the car up the oil pressure shoots up to over 120 lbs and stays there until the car gets warm. When warming up, the idle pressure stays at around 60 psi and the oil temps rise to about 180 degrees. Then I pull out on to the track. On track the max pressure stays at around 50 psi independent of rpm above 6000, but what is odd is that as my rpm drops to under 5,000 the oil pressure creeps up to about 60 to 70 psi or if I reduce the cornering loads it will creep up a bit, but still not exceed the 60 to 70 mark. That is on track only. My oil temps rise to about 240 and then stay there. I am running 20-50 Mobil 1 Racing oil.

What is odd and bothering me, is that when I came into the pits after a 1 Hour Race and let the car idle, the oil pressure stayed at about 60 psi at idle, higher than when it was on track at higher rpm's. When I revved it up, the pressure dropped to about 50 psi. Its almost like there is a pressure relief valve that sticks open at temp and rpm. If it was bad bearings or a clearance issue, I would expect the oil pressure to drop to about 10 psi at idle or something like that. After the car did this in practice, I tried adding more oil to the case about 1 quart above the fill line, but all that succeded in doing was blow the excess oil out the overflow can lid with no effect on the running pressures. Its almost like the sustained rpm causes the car to over scavenge the pan or I have a really bad clearance somewhere and the pump can only cover the leakage to a max of 70 psi hot.

Any ideas as to what could be causing this?

Eric