Oil Pressure Issues Again

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

It would really help to know what kind of car/engine you are talking about.

With those symptoms, the only idea I can come up with is that your dipstick is off and your pan is overfilled. If your oil level is well over, you could then be hitting the oil with the crank and aerating it substantially. This would cause the pressure to drop off at higher revs or Gs, due to increased frothing, and possibly go back up a bit when you back off some. Then when you go back to idle, you start pumping unaerated oil and the pressure goes back to its maximum. As an aside, the 120 cold/60 hot idle pressures seem quite high.

If you haven't redone the pan or dipstick and used to not have this problem, then it's undoubtedly something else that I have no idea about.

Did you check the oil purge valve and any seals associated with the pump installation? Is this a recent issue or something that has always been this way? What changed before you started having this issue? Specifically what maintenance/modifications were made prior to this issue?

Sorry, it would help to know the motor, but I doubt that anybody is racing one of these as I think only 5 race motors were ever built and I own 2 of them.

The motor is a Kinetic Racing Engines built D.O.H.C. 2.5L Ford Duratec. The bottom end is all billet crank, Carillo rods and Wiseco pistons. The pan and pickup were custom built to control surge. It was originally built for the WC Series and made close to 300 hp. When I called Kinetic for information, they were nice but evasive and couldn't or wouldn't provide any build details. It is sorta a black box. They said for me to send the motor back into them for a rebuild at about $10,000.

I have had comments like the pressure relief valve is stuck or the relief valve spring is broken. As well I was told that the pan may have been compressed and the gap between the pickup and the pan is too close and restricting high rpm oil scavenge.

These are all ideas and I am looking for some more ideas before I ripped the motor out again.

No changes were made to the engine lately other than regular oil changes. What was interesting is that the previous owner of the car said that what I was seeing, he battled with as well, but he only ran the car in 6 races. So more than likely, the engine only has about 15 races on it.

If flow into the pump is restricted, pressure will diminish when RPMs increase.
Aeration is a possibility, but I wouldn't expect it to recover so quickly.

Drop the pan, add 1/4 in shim between the pick up and pan bottom. Push the pan back up and see if it hits at 1/4 in. Under 1/4in, you may get some airation of the oil.
1/4 in should be the minimum from the pan to pickup. While you are there, verify the dipstick mark is under the windage tray or crank swing level.
That seems like too much oil prressure. Maybe try the Rotella 5/40 synthetic.
There is a chance of baffles creating some air bubbles near the pickup.IMHO/ MM
It may also have a cracked pickup tube that is vibrations sensitive

you try a different pressure sender and gauge?

make sure they are mated correctly?

+1 on the gauge.

Is it mechanical or electrical?

I was wondering about the sender as well. It is an Autometer Comp gauge set. The sender is situated under the front header and it looks a bit tired. Anyway to test the functionality of the sender? I guess I can send it back to Autometer, but it is a case of diminishing returns as the mail costs and duties are about the same as the sender cost.

Interesting and something to try first. I could just buy a cheap gauge and try that to see if I see the same things.

Great ideas.

Eric

Check with Leo Capaldi. He ran the Cougars in WC.

http://www.capaldiracing.com/index.html

Try changing oil to Valvoline Racing Synthetic 20W50. It is rated one of the best at maintaining pressure at higher temps. Mobil 1, although a great oil, is not rated very high in maintaining pressure at temp. Chuck

The pressure senders seem to die eventually. Depending on the sender it may also be grounded through the threads and a bad ground could give you weird readings. I would try checking with a mechanical gauge to verify the readings you are seeing.

On my latest install I'm not installing the sender directly in the pressure port, but instead running a piece of hose between the port and sender. Hopefully that'll isolate the sender from the engine vibrations some and lead to a longer life. This sender has a ground wire so it doesn't need to be grounded through the threads.

David

Suggestion...manual gauge with -3 or -4 line from block to gauge. KISS. Chuck

I was talking to a friend out in B.C. last night. It seems like he developed the same issue with Mobil 1 and oil pressure about 2 years ago. It seems that after Mobil 1 sued a competitor over their definition of synthetic (they were using a part of the blend based on modified dino oil) and lost, they converted their formula as well to a blend of modified dino oil and a true synthetic. This was less costly and would work for 99% of their customers and still allow them to call the product a synthetic.

He was suffering from loss of oil pressure and viscosity when very hot as well. After talking to his engine builder who confirmed the issue, he converted to Motul 300V and everything was fine and the pressures returned to normal when he was up in the 250 degree area. As a side benefit the oil smelled like maple flavoured bacon. He says that whenever he is driving his car now, he gets a bit hungry and he doesn't know why, LOL.

I guess I need to convert back to Redline Race or Motul 300V. Can we say KA-CHIIING $$$$$$$$. The first few times I ran the car it was with Redline 40 wt Race oil and had no issues. It has only been since I converted to Mobil 1 20w50 that I have been having issues, hmmmmm....... Seems like an easy fix.