gbailey911

Yesterday I took a 500 mile round trip in my 87 Carrera 3.2 to attend my Dad's 80th birthday. It was a beautiful day for a drive, clear skies and 30-40F temperature. The trip went with no problems...except my oil pressure gauge did not seem right. When cold I have seen 5 bars on the gauge with new oil and cold but yesterday the needle was at 5 bars for the first 2 hours as I cruised at 3000 rpms. The pressure would drop to 1.5-2 bars at idle but would rise to 5+ bars once I returned to speed. I stopped after the first two hours for a lunch break, and after re-starting, my gauge was back to what I would call normal at 3.75 bars at 3000 and 1.5 bars at idle. After the party(3 hours off), I started home and the gauge was back to pinned at speed and 1.5-2 at idle. After three hours driving and a short off break, the gauge was back to normal until I got close to home, 1 hour later, and then it went back to pinned at speed.

The car ran perfect the whole trip with the slight distraction of the oil pressure gauge and the temp never went past the 1st line on the gauge. I am running Brad Penn 5w-50 oil if that makes a difference.

Does anyone know what could be wrong or what I should check as I know(think) my pressure is not that high?

As always, thanks for looking and thanks in advance for any thoughts!

dshepp806

I can tell you that my 89 first provided some non-linearity with the BAR/RPM. I immediately installed a new sender and replaced somewiring from the sender up towards the harness. It impoved it, albeit slightly. Mine seems to go no higher than 4.5 and will easily show 4 at 3ooo RPMs sometimes....I'm suspecting the instrumentation now....but have yet to get this resolved.....

Her pressure's checked,..she's got it.......

Did you recently change the oil type?

Do make sure that the sender's not lieing to your instrument,..and that it's cabling is in good shape,..connectors nice and clean/tight (both sender and instrumentation). I found my sender's cable retainer clamp cocked and wearing through the harness to the copper...had to rework this part.

,...pros will chime soon.

Best,

Doyle


..just 2 cents.

rusnak

it sounds like you have too much oil in the tank.

gbailey911

I thought that at first but it is dead in the middle between the lines at full operating temperature.

ked

I'd hope its the sender in the early non-linear failure mode, but I'm an optimist.

Ed Hughes

Oil level will not effect pressure reading......unless it's out of oil, of course!

rusnak

Are you using a Mahle oil filter?

I don't want to be argumentative, but if you have too much oil in the tank, the sump can't suction it all out fast enough and your oil pressure will be too high. You can destroy a catalytic with too much oil being pushed out through the exhaust, or worse. The dry sump will maintain oil pressure within a range of about 1-2 quarts of oil. Beyond that, and the oil pressure will get too low or too high.

Also, I don't know if you can actually get the engine up to operating temp at ambient temps of 30-40F as you mention. Look on the very left edge of your temp gauge for the numerical markings. You might need a strong flashlight. Check your oil temp at a minimum of 180F. Better to check at around 210F so that your oil thermostat is fully open. Let engine idle on level ground at least 2 mins. Check with the oil tank dipstick (do not trust your gauge over the dipstick).

Ed Hughes

I still don't see how a pump is going to over-pressurize the system. If the pick up is immersed in oil, it will pump to its max, whether the level of oil is just over the screen, or 5" over the screen. If there is too much oil in the system, I believe it would manifest itself by excessive smoke, which is not one of his complaints.

theiceman

There is no way you should ever be sucking all the oil out of the tank. This is the reservoir of oil used. There is no way oil level will affect pressure, outside of the weight of the oil itself which is marginal compared to pump pressure. oil pressure is determined by viscosity, pump throughput oil gallary width and resistance at output. Too much oil will overflow into the intake via the brether tube and create a smoke screen.

Although oil in the cats will destroy them i agree, it has nothing to do with the oil pressure itself.

But back to the point at hand.

I too think it may be more to do with the thermostat and the oil beinf rediverted through the cooler. personally i don't think it is really anything to worry about , but that is just my 2 cents.

gbailey911

The oil filter is a Porsche Mahle filter and it was replaced in June with the oil change (only 900 miles ago) and everything has operated and read fine until the other day. I'm thinking it could be the sending unit since it is original and only going on 22 years old. On Pelican Parts, the description for a new pressure sending unit says: " Is your oil pressure gauge reading bizarre ranges? Does the gauge peg at the top? Then you might have a faulty oil pressure sender. Replace your faulty sender with a new one and regain the ability to measure your engine's vital pressure. " This sounds like my car's symptoms but I don't want to buy a sending unit to just throw money at the problem.

Thanks to all in advance!

Ed Hughes

The first thing I would do is check your electrical connections from the sender to the gauge. Then, if it still is doing that, a new sender. Senders are pretty cheap, IIRC.

dshepp806

Yes,..the connection integrity is paramount.

There are some great "autopsy" threads/discussions on this sender and "how" it functions.

My take (while tackling this issue) was to "start" with a fresh sending device.........it would appear that this solved "part" of my issue, but not all. Time to look at the instrumentation side of the circuit, as the cabling looks to be solid.

BIG THING: is what's ACTUALLY happening within the engine. This can easily be measured/quantified, while one pursues the instrumentation errors.

...piece of mind?

Best,

Doyle