Porsche Enthusiasts Club Forum

Well I told you I wouldnt leave this dead.

So ive not done very much, but as the resto on teh VW drew to an end and the weather started to pick up I thought id unwrap the 944. I went for a run after adjusting the belts. Id over tighten the balance belt previously and it had the 944 washing machine note. It was a voyage of education. One the motorway on the drive home I noticed the oil needle start to stablise. For the last 5 miles home all was well once again.

This got me thinking, still along the lines of an OPRV issue. Cold oil=high pressure Hot oil=Lower pressure. So after a good 30 miles covered nice and hot on the driveway engine at idle the needle was reading just over 2 bar. I slowly increased the revs and the oil pressure came up in a linear fashion. It reached 5 bar just after 2000Rpm. Suddenly theres a drop of 1.5 bar with a bit of needle hunting.

The revs continue to rise and the pressure returns to a linear rise to a solid peak of 4.5bar.

So my theory being ive got a sticky valve, and it takes a high pressure to initially operate it. This is what happens at 2000rpm. A pressure much greater than 5 bar (or what ever the specificated releif pressure is) Then once its been unseated the spring is a bit weak hence the hunting to find 3.5bar. But from then on it works as expected and get to 4.5-5bar and bleeds the pressure off as it should.

Who's buying that? And does any one have any tech info on the valve, at what oil pressure should it start to relieve pressure?

Before you start trying to figure it all out with the notoriously dodgy electric pressure gauge, I would rig up a normal oil fed gauge

There are two types of OPRV and they can be cleaned and new O rings fitted, as they are serious money for a little valve

But if you generate much more than 5 bar you will blow the seal out of the base of the oil filter, another problem that seems to appear is the oil filter housing goes out of shape and jams the OPRV, seen this happen twice now, the first time at brands with a big cloud of smoke and a fire ball on the short straight

And that housing is over £600,

Yeah ive well covered all the gauge, wiring and sender stuff. Theres a fair few videos earlier in this thread. The engines always had cracking oil pressure. As you can see in the videos at cold its as high as 6.5 bar at times (id assume the valve should have operated by then). Once warm its still heading towards 5. Its the old 3 piece style valve.

But your second comment intrigues me. I have over the winter bought a second hand oil cooler housing. At some undetermined future date, I do intend to fit this. Maybe it could be the cure?

Id still be interested in some specs to help understand when the valve should operate.

One interesting trait which ive yet to reconcile in my head is cursing along at constant speed constant throttle I could for example see around 4.5bar oil pressure. I then do nothing but press the accelerator pedal to the floor and for the duration of acceleration the oil pressure will drop to around 4 bar. As soon as I lift of the throttle it will return to 4.5.

Given that oil pressure is proportional to RPM. Other than a little extra loading on journals the throttle really has nothing to do with it.

Ok so reading the manual, the Oil pressure sould be 4 BAR at 5000 RPM at 80 Degrees C. 58psi

It does not give absolute values for the valve,

thinking about the throttle pressure drop, its going to be very hard to explain that one, the only thing that springs to mind is a huge increase in crankcase vacuum slowing down pickup.. but other than that its a mystery for now.

the housings that were a bit suspect were very difficult to get torqued down after gasket replacement and still allow the alignment tool to move, once placed on a surface plate it was clear to see they were a bit wonky, only by a few 1000th of an inch but enough to cause an issue,


a new OPRV for 9442 1987>> £365.50, the housing £586.32

I will take a look at the car ref these specs . 80 degree oil temperature?

Very interesting thoughts regarding the pressure drop. I may disconnect the case vacuum out of curiosity for a short run, just to see if i still get the same effect.

I will do some more GoPro videos, hopefully over this coming weekend and see what else we can learn. I love a bit of bitty gritty detail. The oil pressure is still happily above spec so I'm not overly concerned. I'd just like to fully understand my engine.

I will measure this new housing I've got. I simply can't afford a new one. Though i may be heading for a new valve at some point.

Good info, much appreciated

Many many months later, this was all down to the OPRV and a tiny lip which has formed inside the block. So the 3 piece style valve needs to be replaced with the one peice assembly at some point. But it has improved somewhere with a little care an attention when I reinstalled the cooler housing and spent some time aligning it. The pressure never drops below spec. It just runs a little high at times. But this winter I plan to pull all the running gear off the car for a general refurb and have the body repainted. So ill invertiage and repair properly with the engine out.