I have some ideas, but there are probably more out there. I recently purchased a 1985 Carrera with 88K miles. It has been driving fine with oil pressure gauge registering PSI directly related to RPMs (1,000 rpm = 1 on the guage - 5,000 rpm = 5 on the gauge).

At start-up the other day I noticed the pressure came up but failed to increase with RPMs. It may have reached 1.5 on the gauge while I took a nervous drive. Idiot light never came on or flickered. I run 10-50 synthetic oil (its hot in nor cal). Oil level is in the middle of the markers at idle. Oil temp was normal. I checked the connection from the sending unit and noticed a very slight amount oil near the sending unit but not on the unit (the engine is very clean).

I have also notice that the oil level gauge tends to drop occasionally into the red while driving.

I think it could be the sending unit or possibly a ground. I don't think it is a clogged oil filter or oil pump pick-up.

There was absolutely no hint of a decrease in performance.

Any other ideas out there?

 

Jeff:

You might have:

1) A bad pressure sending unit. This is located near the front of the engine just above the bellhousing and to the right. The sending unit to the right of the fan next to that oil line is the temperature sender,...

2) Sticking oil pressure relief valves. These are located at the bottom of the engine case. Get a copy of the Bentley Carrera manual to make a positive ID and see how they are assembled. These can be carefully removed and cleaned.

3) Don't worry about the oil level guage; the dipstick is Gospel.

Never use an American oil filter. Always,...always use the proper German filter. A Mahle or Mann is just fine.

Change that oil every 3K-4K miles and it will last a VERY long time.

 

Steve has it right (of course!). The dash gauge seems to be working as it should - accelerating will drive the oil pump harder and pull oil out of the tank (the gauge will drop, often to zero), cruising will allow the tank to refill and the gauge needle will rise. There is only about 2 litres from max to min on the gauge so is only an 'indicator' of oil level.

PJC

 

I cerainly would not mess around with this as the results could be disasterous if you guess wrong. For the money invested I would remove the oil, change the filter , remove the sump cover and inspect and clean , remove the presure bypass valve clean and inspect, replace pressure sending unit or at least check it with an appropriate pressure guage . My 78 has a pressure sending unit to the right of the Fan in the rear beside the temp sending unit, but yours is much newer and may be different, Steve is the expert here.
My only real point it when it comes to oil pressure assume the worst and work backwards. It is a much better bet than assuming you have a bad sensor and being wrong !

Good Luck.

 

ice: No sump cover on an '85! However, you're correct to be concerned regarding the problem. My uncertainty is - Jeff, are you also using the dipstick on a regular basis? I have seen owners come in six quarts low, and say, "but the guage works...". For what it's worth, Steve's first comment is consistent with my first thought - the sending unit has probably failed. I've seen a number of them go bad, and it's almost always diagnosed by the symptom that you describe. However, if you haven't been, check that oil level with the dipstick!!!
Pete

 

Thank you all for taking the time to respond. I've ordered a new sending unit as a start. I didn't even know about the relief valve. Is is accessible without pulling the engine?

Regarding using the dip stick to check oil, I do and couldn't agree more...that gauge drives me NUTS!

Lastly, the low oil pressure really freaked me out. This is my first Porsche and I loathed the thought of blowing the engine in such a beautiful machine...and after only owning it for four months! I will treat this issue with the utmost care. Lets hope its just the sending unit!