Carpokes Porsche Forum

1987 Turbo w/ 170K miles. I purchased the car about a year ago. Ever since I've owned the car, I would get 5 bar of oil pressure on the dash gauge when cold. However, now matter how hot the motor would get, it would never go below 3.5 bar.

Given the milage, I don't want to risk having bad bearings and I really don't want to have to replace them unless they really need it - so I really want my dash gauge as accurate as possible.

Step 1 - Clean all grounds under the dash
Result - no change

Step 2 - send an oil sample for testing
Result: Passed with flying colors

Step 3 - Replace OPRV w/ Porsche unit
Result: Now cold start results in 4 bar oil pressure and goes down to 3.5 when warm? When revving the motor, it will go back to 4 bar and not any higher

Step 4 - Replace oil pressure sending unit w/ genuine VOD one (what a terrible and frustrating job)
Result: No change from step 3

I'm baffled and I do not have a mechanical gauge to get actual pressure readings. If I did, I would absolutely dread having to pull out the sending unit again. Any thoughts?

3.5 bar at warm idle is excellent especially if using anything thinner than a **W50 oil grade.
The pressure however should read between 4.5 and 5 bar under load. Where did you source the new sender and do you have access to a known old working unit to make a comparison?

Thom wrote: Fri Jan 26, 2024 1:35 pm 3.5 bar at warm idle is excellent especially if using anything thinner than a **W50 oil grade.
The pressure however should read between 4.5 and 5 bar under load. Where did you source the new sender and do you have access to a known old working unit to make a comparison?

I run Valvoline VR1 20W-50 and the oil is pretty new. The only other sender I have is the original one I had, which never dropped below 3-3.5. I got the new sender from Pelican. I would suspect the gauge itself, but I had sent it out for a full service last spring (mainly to fix the fuel gauge calibration).

NCGermerican wrote: Fri Jan 26, 2024 3:01 pm

Thom wrote: Fri Jan 26, 2024 1:35 pm 3.5 bar at warm idle is excellent especially if using anything thinner than a **W50 oil grade.
The pressure however should read between 4.5 and 5 bar under load. Where did you source the new sender and do you have access to a known old working unit to make a comparison?

I run Valvoline VR1 20W-50 and the oil is pretty new. The only other sender I have is the original one I had, which never dropped below 3-3.5. I got the new sender from Pelican. I would suspect the gauge itself, but I had sent it out for a full service last spring (mainly to fix the fuel gauge calibration).

What is your concern about your readings? They sound fairly typical to me? What are you hoping to see? Or am I missing something? See Clark's, for example, that says oil pressure is typically 4 or 5 at idle when cold and gradually drop to 2 or 3 when hot. (The hotter the motor, the more it drops, just hopefully not below 2.) Idle speed can also play a role -- a high idle will generate more pressure than a low idle. Outside temp and oil weight play a big role in pressure too, especially during warm up.

https://www.clarks-garage.com/shop-manual/lube-03.htm

Tom wrote: Fri Jan 26, 2024 3:26 pm
What is your concern about your readings? They sound fairly typical to me? What are you hoping to see? Or am I missing something? See Clark's, for example, that says oil pressure is typically 4 or 5 at idle when cold and gradually drop to 2 or 3 when hot. (The hotter the motor, the more it drops, just hopefully not below 2.) Idle speed can also play a role -- a high idle will generate more pressure than a low idle. Outside temp and oil weight play a big role in pressure too, especially during warm up.

https://www.clarks-garage.com/shop-manual/lube-03.htm

My concern is that after I changed my OPRV for a brand new one, I would get 5 bar oil pressure when cold and under acceleration. Now, it shows 3.5-4 bar on cold startup and pretty much stays there when warm.

NCGermerican wrote: Fri Jan 26, 2024 6:42 pm
My concern is that after I changed my OPRV for a brand new one, I would get 5 bar oil pressure when cold and under acceleration. Now, it shows 3.5-4 bar on cold startup and pretty much stays there when warm.

Hmmm.... Did you use an OPRV alignment tool? Which version of the OPRV are you using?

Tom wrote: Fri Jan 26, 2024 7:25 pm
Hmmm.... Did you use an OPRV alignment tool? Which version of the OPRV are you using?

I didn’t use an alignment tool because I wasn’t removing the housing- just taking out the old OPRV and installing the new one. Both are the later, one piece versions. The o-ring on the old one was totally flat, so I’m shocked that the new one would be functioning incorrectly, IF that is the issue.

Make your life easier and verify the oil pressure with a mechanical gauge.

If the stock and the external gauges agree and if you think the OP is off, then take another look at the OPRV.

If the mechanical gauge shows different values than the stock gauge, then look at the sending unit, wiring and the dash gauge.

To check the dash gauge, you can use s potentiometer in place of the sending unit. I believe Clark's garage talks about this.

On a cold engine, I see 5bar. Also running VR 20W50 oil.

Fast951 wrote: Fri Jan 26, 2024 8:34 pm Make your life easier and verify the oil pressure with a mechanical gauge.

If the stock and the external gauges agree and if you think the OP is off, then take another look at the OPRV.

If the mechanical gauge shows different values than the stock gauge, then look at the sending unit, wiring and the dash gauge.

To check the dash gauge, you can use s potentiometer in place of the sending unit. I believe Clark's garage talks about this.

On a cold engine, I see 5bar. Also running VR 20W50 oil.

Thanks John - I'm going to bite the bullet and do as you suggested. I bought a mechanical oil pressure gauge and it should be here this weekend. I'm just irritated as it seems I should have left it all alone to begin with.