Low to no oil pressure...

[saturnine_sweet]

This is the problem: About two weeks ago, the oil pressure began to drop to zero once the car warmed up. At first, it was intermittant, and the pressure would always begin at 60. Now, it ALWAYS drops to zero, and starts no higher than 30. I've changed the oil, and the oil pressure switch, to no avail. The car (96 3800) seems to run fine, sounds normal, etc. So I was wondering if anyone had any ideas? I've heard something about a pressure relief valve? What else could cause this? Thanks in advance.

[98 3.8]

Re: Low to no oil pressure...

My car's oil pressure often goes under 30, especially when I'm due for an oil change and the oil is thin. It doesn't worry me a whole lot though...


Does the pressure rise when you rev the engine?

[saturnine_sweet]

Re: Low to no oil pressure...

the pressure rises under load, though no higher than 30...at idle, once warm, it sits at zero....the oil is fresh, 10-40...

[saturnine_sweet]

Re: Low to no oil pressure...

I dug deeper into the board, and found the valve I was thinking of is called the oil pump bypass valve...can anyone supply some info on this? What does replacing it entail? What parts are needed, and where is a good place to purchase them? Thanks!

[Rob Bell]

Re: Low to no oil pressure...

Before you go tearing things apart, try hooking up a known, good mechanical oil pressure guage so you can be sure exactly what the oil pressure is. Don't just rely on the dash gauge. You may find that there is nothing wrong...... or you may confirm that there is a problem.

[saturnine_sweet]

Re: Low to no oil pressure...

sorry, forgot to mention, I have done this since changing the pressure switch...its right on the same as the electronic gauge reads...around 30 max, 0 at idle...

[saturnine_sweet]

Re: Low to no oil pressure...

checked the valve today, looks to be a new part, has no wear, moves freely...so what am I looking at now?Oil pickup tube or screen clogged? Any other possibilities?

[Nikos95]

Re: Low to no oil pressure...

Before you go tearing things apart, try hooking up a known, good mechanical oil pressure guage so you can be sure exactly what the oil pressure is. Don't just rely on the dash gauge. You may find that there is nothing wrong...... or you may confirm that there is a problem.

Do exactly this! The electrical gauges, and sensors don't work worth a ****! Never trust a thing your factory oil pressure gauge says.... They are horribly wrong! Test it with a good mechanical one and see how it runs. If its good no worries, replace the sensor or gauge if you want.. Personally I'm taking mine out , and fabricating a new dash panel there for new mechanical gauges, and a few added gauges, including a full size tach and 180mph spedometer.

[CDNFB]

Re: Low to no oil pressure...

What about the spring that holds the bypass valve closed? How close did you look at that? It should hold the valve closed untill approx 70 psi then it opens and bypasses the the oil back to the inlet side of the pump. Kind of like a regulator. It's nice that the valve moves freely, but if the spring is weak or damaged then it can open and bypass at lower pressures.

so what am I looking at now?Oil pickup tube or screen clogged?

Yes, those are possibilities. Also:

1) worn oil pump
2) Worn crank main bearings or other worn internal components that are creating excessive internal oil leakage.
3) oil gallery restrictions or blockages.


4)

[slow6]

Re: Low to no oil pressure...

or other worn internal components that are creating excessive internal oil leakage.

that would be bad piston oil control ring
what else could have internal oil leakage?

[CDNFB]

Re: Low to no oil pressure...

But the oil control ring(s) is(are) very evident by the blue smoke out the tailpipe and the fouled spark plug(s). I've never seen oil control rings as the primary cause of low oil pressure. Excessive oil consumption.. yes. But not pressure problems.

what else internally? Either individually (when worn in extreme excess or in combination:
- Worn lifter bosses
- worn crank bearings
- worn connecting rod bearings
- leaking oil gallery spacer plates (not on a 3800) but that crappy 4.6 nothstar does! (and that is a whole other long sad story!!!)
- oil pump attachment loose and not sealing
- oil leaking from head gasket into lifter valley

[saturnine_sweet]

Re: Low to no oil pressure...

thanks for the help. I dont think it is anything leaking, as I do not lose any oil, that I have noticed. As for worn bearings, same deal, I doubt that because it was a sudden change. I went from have good PSI, to back and forth for a few days, and now nothing, basically. In my experience, which might be wrong, but usually worn bearings, you see a gradual drop, more than a huge, sudden drop. Also, my car has the oil gear setup, rather than a true oil pump. I thought this might have gone, but, with how the increase in PSI with engine load is consistent, I doubt it. If there was a slippage issue with the oil gear, I would think the PSI increase under load would be erratic at times, no?
Finally, as for the spring on the oil pressure valve...again, where I experienced a sudden loss of pressure, I find it unlikely that its a spring that is a little sprung. Again, that would generally have more gradual symptoms.
Also, I have no other problems with this car at all. Other than no oil pressure symptoms (ticking,) it runs beautifully. No smoke in the exhaust, or anything. There is a small trans fluid leak, but I know where it is coming from, just havent fixed it yet. Does anyone know what kind of cost I would be looking at, if I took it in to get the oil pickup and screen serviced? I dont have access to an engine lift, and dont especially feel like doing it with the driveway method lol Thanks again for all the help!

[saturnine_sweet]

Re: Low to no oil pressure...

CDNFB- oil pump attatchment loose and not sealing? I am not sure what you are referring to there?

[CDNFB]

Re: Low to no oil pressure...

What I mean is the oil pump assembly loosening off and leaking.

I've seen oil pumps (driven by the camshaft, gear type pump) in older engines where the attachment bolts were loosened off and oil was leaking at the pumps attachment to the block.

Our engines have a direct crank driven oil pump (gerotor type pump) behind the timing cover. If any of the pump assembly bolts have loosened off there will be leakage back into the oil pan.

usually worn bearings, you see a gradual drop, more than a huge, sudden drop.

Unless your experiencing a rapid failure of a bearing or bearings, or even your oil pump.

There has to be an explaination as to why your oil pressure suddenly dropped. Something is wrong. You've looked at most of the easy things and mechanically confirmed low oil pressure. Now you have to get into the difficult stuff, and it might lead into a removal and complete dissassembly of the engine.

I would start with the oil pickup screen and tube. Also make sure the oil pickup tube is not loose and sucking in air. Then I would look at removal and dissassembly of the oil pump and do a visual and dimensional check of the pump components. Then after that, as ugly as it is, your into tearing down the engine.

[CDNFB]

Re: Low to no oil pressure...

I dont think it is anything leaking, as I do not lose any oil

That's for external leakage (out of the engine onto the ground or adjacent areas)

An internal leakage will return to the oil pan and oil level will not be effected, unless it leaks into the cooling system, but that's not a problem your having (hopefully)