nocomment

I recently rebuilt the motor in my 944 and everything is running great but I have some concerns about my oil pressure. The max oil pressure I see hot or cold is about 4.2 bar on my gauge throughout the rev range(about 2.5k RPM and up) and I assume that's where my OPRV is opening. I read around that the OPRV should open closer to 5 bar. I have the original 3 piece OPRV and would like to shim it. Does anybody have information on how thick of a shim I should start with? I assume the washer goes inside the cap to push the spring out further making it stiffer?

Some information and concerns:
When I push the car hard on these 90 degree days I see an idle pressure around 1-1.2 bar. Never drops below 1 bar. I still get 4.2 bar at 2.5k RPM, and also 4.2 bar at idle when cold. I read some conflicting information of people who say this is a safe oil pressure at idle and others say that when hot i should be getting around 2 bar at idle. I'm currently using a 20w-50 conventional oil. The intake fitting for my oil cooler is hot while the exhaust fitting is cool, and the cooler itself goes from warm to cool across it, so i assume the oil cooler is working. Is it possible the weak spring in the OPRV is causing the lower idle pressure? Is it possible my oil cooler thermostat is not opening and only allowing the minimum oil to pass through so the oil is over-heating(I did have the thermostat out of the car before and everything looked good and moved freely)? Maybe my oil pressure sender is reading slightly low? Am i just being paranoid?

I will probably start by shimming the OPRV and switching to a 10w-40 synthetic oil since neither of those things could hurt? and go from there. Thank you all for your time.

mahoney944

You should probably hook up a oil pressure gauge and see what your actual pressure is to eliminate a faulty cluster, wiring, sender, etc.

nocomment

Is there a way to hook up a mechanical gauge temporarily as a tester?

jimbo1111

I had a similar issue on my last 951. First check the torque on the crank as the pump rotates based on friction. If it isn't torqued properly then there is a chance of slippage.

My issue was the pump. After running hard on track the oil pressure fell below 1 bar at idle. I thought the 20-50 oil put to much of a load on the seals. I don't think I'll be using it on the new car.

nocomment

I’ll re-torque the main bolt since it’s not hard to do, although I did torque it to 150 ft/lbs when I rebuilt the motor. I also read that 10w-40 is ideal for the track since it flows more and the synthetic oil molecules are better at moving heat since they have more surface area.

nocomment

So i went ahead and shimmed my OPRV, I used two washers that fit inside the head(they came off the 10mm water pump bolts i had laying around) and my oil pressure increased from 4.2 to 4.7 bar. I haven't had the car hot enough yet to see if idle pressure increased. Here are some pictures(parts disassembled, cap before washers, cap after washers)

nocomment

EDIT: there is something def. wrong with my gauge, after i shimmed it the oil pressure when warm was reading the same as my oil pressure on cold start without shims because the gauge maxes out at 4.7bar. Idle pressure read about the same when warm. I know the gauge needle can move the full range(reversed the connections on the sender) so its not a cluster issue, so unless the length of the wire matters like it does for the O2 sensor(I had to re-do a lot of the wiring to the sender) then the sender is bad. Either way I will be installing a mechanical oil pressure gauge.

s85b50

Does '89TT with a one-piece OPRV need a shim?

nocomment

You cannot shim the one piece styles, only the 3 piece since it comes apart like in the photos above.