High Oil Pressure and OPRV Questions

[DaddyGlenn]

944 Spec race car, engine has a 1983 block, stock NA oil cooler. Had a couple oil related problems. Several oil leaks and the Autometer oil pressure gauge would peg over 100psi, anytime the engine was running.

I replaced all the front seals but still had an oil seeping from near the oil pan gasket under the lower balance shaft. So I changed the oil pan gasket.

With the oil leaks resolved, I hope, I turned to the oil pressure gauge. I checked continuity of the wires between the gauge and the sender. They checked out. So, I assumed the problem was in the sender or gauge. (Autometer is very proud of their gauge and sender $$$$) I replaced the gauge and sender with known good stock units. Same result, gauge pegged to the high side.

So now I realize have an oil pressure control problem. I pulled the OPRV. It is a 3-peice unit that appears to be in good condition. But I found 2 M6 washers under the cap. Guessing someone before me, tried to boost the oil pressure using washers as spacers. I removed the washers, reinstalled the OPRV and started the engine. This time, no oil pressure.

So I scrounged the garage for other OPRV to compare spring lengths.

I found 2 others to compare with. One had a 17mm hex head and the other had the same 8mm allen head as the one on the race car. Spring size on all three was the same and each "felt" like they had the same compression strength.

What was different was the 17mm hex head had a deeper pocket in the top piece. When assembled, it was significantly shorter. See pictures below.

Does anyone know what engines these two different length OPRVs are used for?

And any ideas on what is causing my oil pressure problem?

Could this be an alignment issue with the oil cooler?

[wildcat077]

Glenn,

Do yourself and your car a BIG favor and purchase a new updated one piece OPRV ... unless you want to burn your car down due to an engine oil fire.
I've had two oil fires with the three piece OPRV , once with a Canton oil filter and housing and another time with a Porsche filter.Both times the oil pressure pegged over 80 PSI and blew the gasket out of the filter.Anyhow , i went to the dealer and purchased a brand new OPRV which solved that issue !

Cheers
Phil

[wildcat077]

You don't want this ... it's $300.00 dollars every time i discharge my fire system, half the price of the new OPRV !
That was on the first lap, not tire smoke but oil that blew off on my header and caused a fire under the hood,i couldn't see anything inside the car ...

[TheSecondChris]

I wish I better understood the operation of this valve. Based on my limited understanding, it seems like it is not sliding properly and first got stuck closed leading to high oil pressure and then got stuck open leading to low oil pressure. So either there is some kind of foreign object or scratch preventing smooth operation, or poor alignment as you suggested.

It seems there are several flavors of oprv that fit the early cars including variations of the spring and cap used in the 3 piece style, and then ultimately the 1 piece retrofit. I found this tech bulletin addressing a change to the 3 piece, but there may have been other versions as well.

[walfreyydo]

You need to be sure to have the oil cooler housing aligned properly with the special alignment tool, or the OPRV will bind (either fully open or fully closed). The key is you need to align the oil cooler housing properly when reinstalling it. All of the info about the newer OPRV, differences in early vs late and proper alignment procedure is outlined in clarks-garage so no need to explain here.

I second what others have said about purchasing the newer one piece unit.

Also keep in mind that normal oil pressure at cold start (at idle) is 5 bar which equals 72.5 psi of oil pressure and decreases to 2-3 bar when fully warm. 1 bar = 14.5 psi

[DaddyGlenn]

Found my alignment tool. Alignment is good. Fortunately, I was able to find a used 1 piece OPRV in excellent condition for a fraction of the new price. Got it installed and oil pressure is where it should be.

Thanks all!

[walfreyydo]

Awesome to hear and thanks for the update!