Can you explain this oil pressure finding?

[bpu699]

We know that oil pressure is a function of oil viscosity, temp, and flow...basically.

So, if your bearings or pump have wear, oil pressure may be low. But, wouldn't it still be proportional to RPM?

I see posts on here that go something like this:

At 1000 rpm, 1 Druck (15 psi or so)
2000 rpm 2 Druck
3000 rpm 3 Druck
4000 rpm 3 Druck
5000 rpm 3 Druck
etc...

Seems like at 3000 rpm the pressure peaks, and the flattens out... My first 911, a 76 with 120,000 miles did that...

Now, my 88 930 with 60,000 miles does also. At idle 1.5-2.0 Druck... Then it rises with RPM to about 3000 rpm then it flat lines at 3.5-4 Druck...

Now, I would think that bearing/pump problems would be proportional. IE, the peak pressure is lower than normal, but remains proportional to rpm...

What causes the plateau effect? Does that suggest a guage/sender issue? How can one have a great idle pressure, that shows this effect? I saw several other posts on here showing the same effect. I have a mechanical guage on order.

When I recently changed the oil, castrol gtx 20/50, for the first 1 minute my idle pressure kept rising until it hit 4 Druck. Then it was like a valve opened, and it plummetted back to 1.5 Druck.

I replaced one of the relief valve springs (the one on the bottom of the case. No big change. I didn't replace the one on the side of the case (the emegency relief valve?).

Changing the sender made no difference...

So, what causes plateauing?

[911st]

There is an oil relief valve on the motor. Oil pressure increases with RPM until the pressure setting of the relief valve is reached then it kind of stabilizes.

On my 3.2 I see above 4 bar at mid to higher rpm.

Years ago wasted two fresh builds on a factory 2.4S motor (cross drilled crank the second time) because the tuners did not check my oil pressure settings.

Thus, I do not know what spec is but you might check it against your motor to be sure you are ok.