Oil warning light comes on under 1000 RPM

[Dave2001S]

Any idea why the oil pressure warning light would be coming on as the car idles under 1000 RPM? Above 1000, it goes away.

[blue62]

Originally Posted by Dave2001S

Any idea why the oil pressure warning light would be coming on as the car idles under 1000 RPM? Above 1000, it goes away.

Most obvious is low (insufficient) oil pressure at idle. Seems to be supported by the loud tapping mentioned in your other post.
Could be an issue with the oil bypass valve. I think on these engines it is located in the oil filter canister. Perhaps another poster can confirm this.
Could be an issue with the oil pressure sensor.
Could be a worn oil pump.
Could be a clogged screen on the oil pump pickup tube-screen.

First think I would try is to buy a new oil filter canister with new bypass valve.
Easiest cheapest simplest.
If that doesn't correct the problem then go to the next easiest possibility to correct.
Work your way up the difficulty ladder.

[thstone]

I agree, insufficient oil pressure at idle. I had suggested checking the oil level but I just read the other thread and you've got that covered.

Blue62 provided a very good list of potential causes and you'll have to work your way through them.

Be careful with this situation, it can lead to big engine problems. Ask me how I know.

[blue62]

Originally Posted by thstone

I agree, insufficient oil pressure at idle. I had suggested checking the oil level but I just read the other thread and you've got that covered.

Blue62 provided a very good list of potential causes and you'll have to work your way through them.

Be careful with this situation, it can lead to big engine problems. Ask me how I know.

Yes if it was my car I would not drive it I would only start and run it briefly after changing or testing something until I had proper oil pressure at idle and through out the RPM range.

[Dave2001S]

Thank you so much, very helpful!

[Chi-Town]

Usually a sign of a bearing issue

[thstone]

Originally Posted by Chi-Town

Usually a sign of a bearing issue

That was certainly the case when the engine oil pressure light came on in the photo above. The engine experienced total failure about 30 miles after I took that photo.

[AZ986S]

I chased that same problem for some time, because the engine would seemingly run and did not make any funny noises. Tried a new oil filter, new oil pressure relief valve, new oil pressure switch, thicker oil...

The issue was much more serious (broken valve retainer that got swallowed up by the oil pump). Dropping the oil pan was what provided positive diagnosis. Ended up putting in a new engine.

So, yes, as has been mentioned in previous posts, low oil pressure could be a sign of more serious issues, so I would not drive the car.

[thstone]

Dave2001S - Any update on this issue??

[Dave2001S]

Thanks for checking back. Not really. I changed the oil again, used 0W40 this time, and added a can of Liqui Moly anti friction additive (just because). Started the car a few times, let it idle, but I haven't taken it out for a drive yet. There is a brief rattle upon startup, but it goes away as soon as the engine turns over. The car sits there and purrs.
It takes longer now, but the oil light does come on after awhile. I was told by my indy, and others here, that the symptoms suggest bearing damage. Don't know what to make of it.

[seningen]

Originally Posted by Dave2001S

Thanks for checking back. Not really. I changed the oil again, used 0W40 this time, and added a can of Liqui Moly anti friction additive (just because). Started the car a few times, let it idle, but I haven't taken it out for a drive yet. There is a brief rattle upon startup, but it goes away as soon as the engine turns over. The car sits there and purrs.
It takes longer now, but the oil light does come on after awhile. I was told by my indy, and others here, that the symptoms suggest bearing damage. Don't know what to make of it.

Unfortunately it sounds like you've got some more serious problems.

Eventually more clearance will occur and you'll have the the light come on at higher RPMs and
eventually spin a bearing due to too little oil.

I lost a 951 engine this way (PO had spun a bearing, and had the engine fixed), it would
only start having issues with older oil, or very hot. Eventually I lost the engine.

Rebuilt it, but would still have low oil pressure when warm -- took me 2 years to figure out
the cam tower had been scored during the first engine failure and never noticed/fixed.

In the interim, I put a new engine in the car.

After replacing the cam tower, I sold it the engine to a friend and that engine still serves my buddy who flogs it at the track with 375HP!


I'm not sure its worth rebuilding a 986 engine at this stage -- you could just drop a junk yard engine for a few grand.

Mike

[thstone]

Originally Posted by Dave2001S

Don't know what to make of it.

Options:

1. Fukc it. Just drive it. If it blows up, then it blows up. And if its the bearing, its not going to take long, maybe just a few hundred miles. If it makes it to 1,000 miles, then its probably not a bearing.
2. Get another opinion. Contact a couple of the best Porsche shops you can find. Talk to them. See what they say.
3. Test and evaluate. Follow the test procedure outlined by Blue62. Replace the oil pressure sending unit. Check the wiring. Drop the oil pan. Do a compression and leak down test. Have an oil analysis done. Or anything else a Porsche professional might recommend.
4. Repair or replace. Tear it down to find the problem and repair or replace the engine with a used engine.
5. Park it and deal with it later. Or maybe never. Might not be the best option, but it is an option. Park it in the corner of a garage and forget it.
6. Sell. You could sell it "as-is". Most buyers will assume the engine is toast and offer ~$4K for the rolling chassis. At least then it's someone else's problem to figure out. If it was me, I would sell it for $4k and then find out later that the new owner figured out that it was just a wiring problem. But that is just how my luck goes.

[Dave2001S]

Option 6 is officially on the table.

[Gilles]

Originally Posted by thstone

Options:
3. Test and evaluate. Follow the test procedure outlined by Blue62. Replace the oil pressure sending unit. Check the wiring.

I would start with Tom suggestion, as this is not really expensive and a failing oil pressure sensor will drive you nuts..

[blue62]

Originally Posted by Dave2001S

Thanks for checking back. Not really. I changed the oil again, used 0W40 this time, and added a can of Liqui Moly anti friction additive (just because). Started the car a few times, let it idle, but I haven't taken it out for a drive yet. There is a brief rattle upon startup, but it goes away as soon as the engine turns over. The car sits there and purrs.
It takes longer now, but the oil light does come on after awhile. I was told by my indy, and others here, that the symptoms suggest bearing damage. Don't know what to make of it.

Yes it could be bearing damage.
But it could be something else as well.
I don't think you mentioned mileage????
Until you do a methodical evaluation-diagnosis and find the root cause your just guessing.
Even educated guesses from experienced mechanics are still guesses until proven right or wrong.

Do the simple things like pull the sump pan and see if there is excess wear particles present. Could indicate excess bearing wear.
Check the oil pump pickup screen. could be clogged.
Check the oil pressure relieve valve. it could be malfunctioning.
check the oil pressure sensor-sender and wiring. could be an issue there.

Assume nothing.
Prove or disprove the rest