Hi there - I have a 91 Camaro with a 305 and 119,000 miles.

My oil pressure has been low the klast few days. The first thing I did was check the level which is fine. I have no means of checking it any other way; I have no gauges, and am not very mechanically inclined.

Typically, when I start the car, the psi is @ 60 - now it is at 30. And it slowly decreases to about 15 as the engine works up to operating temp. It will stay at 15, and flooring the gas on an open road does not bring the pressure up - which it used to. Otherwise, everything is fine - no wierd noises, no sputtering, no stalling, nothing. The only odd thing is that when I turn the air on, the oil pressure gauge spikes down into into the red, and then snaps back up when I hit the gas.

Is this indicative of a bad fuel pump, or possily something else?

Thanks in advance for any ideas.

 

It could be due to many things, including diluted oil, or worn bearings. Try an oil & filter change, and considerting the mileage, use a hevier grade oil, somthing like 10W40, or even 20W50. If this does not work, you will have to look for a mechanical problem.

 

I don't always trust an old oil sending unit either, and have had one lie to me with a hot engine. You might want to consider a new one, before you start to dismantle the engine.

 

90% of the time when a customer has low pressure on the gage and no other symptoms the problem is in the gage system not the engine. When the gage reads low and there is a valve tap or a knock or any new noise that’s when you got an issue. Those gages where unreliable when they where 2 years old. I can not imagine they have gotten better with age. You need to get a real hand held gage on the motor.



http://www.harborfreight.com/engine-...ter-92687.html

 

Thanks for the responses - much appreciated.

So, I was due for an oil change soon, and went and had one done today. A bit early, but that's ok.

I spoke to the mechanic, and he suggested the same as above, to test the pressure with a real guage. He told me it's possibly the pump, possibly the send unit, possibly the guage - and he gave me a doomsday scenario of a "clearance issue". I didn't think I wanted to ask what that was, but couldn't help myself. He started to explain it to me - might as well have been in Klingon...LOL Bottom line is, if it is in fact the worst case scenario, that would require rebuilding the engine, which I guess goes back to z28pete's comment of "worn bearings" - that correct?

Well, he didn't have time to do the test, so I will take it back to him Tues. Thing is, it's gotten a bit better. 30 psi is now about 40, and 15 is about 20. Still too low for my liking, but the other thing - no more spikes down into into the red when the compressor kicks on. Based on the fact that it has gotten a bit better, I - yep, the non-mechanic - would like to rule out any internal engine trouble. Or is that being a bit too optimistic at this point?

Thanks again for the time!

 

If oil pressure is low, then you change the oil and the pressure raises noticeably (like yours did) it usually means you have internal wear issues (worn bearings). You could even throw in a quart of thicker oil, after removing a quart of the old stuff. Or put in some oil treatment (motor honey type stuff) which will help to raise the oil pressure due to it's thicker viscosity. I would still like to test the gauge against a mechanical one to know if it can be trusted or not.

 

Just another FYI. As engine wears the oil pressure drops. Its a normal part of the engines life.

A very sudden drop can indicate a problem. A sudden drop after say the car over heated or after a car ran low on oil would indicate the problem damaged the motor. But even that does not indicate the need for a rebuild.

Each manufacture has it minimum pressure. I use 10 PSI per 1000 RPMs. IMO is you have less then that then your motor could damage itself in normal use. Assuming your gage is correct those numbers would not indicate a need for a repair. I would have cut your old oil filter inhalf to see what was in there. If it is full of metal shaving combind with a "real" drop in pressure I would suggest a rebuild. (Like your mechanic I would not have cut the filter until I proved its not just a gage issue) If it was "normal" filter content I would just suggest you step up your oil weight as stated above.

 

Really? Ick.

But allow me to ask - if there is no other symptom, no performance difference, no noises/knocking/pinging, it can still be the bearings? Wouldn't worn bearings - or some other internal engine issue - show some other symptom(s), or is low oil pressure really the only symptom?

And thanks for your post, Gorn.

Cheers.

 

Bearing tolerances is what dictates oil pressure. Tighter between the bearings and journals = more oil pressure, looser = lower oil pressure. Having the pressure get lower after the engine warms up is normal. How much it drops depends on how much wear the engine has. Your final pressure is just lower than "optimum". Where you're at isn't critical yet, so I wouldn't sweat it, especially since your engine sounds solid (by your description of no noises). What I would do though, is use a thicker viscosity oil than what you have been using. That will give you a thicker cushion of oil between the bearings and journals, and also raise the oil pressure.

 

^ that explains alot - thanks a bunch!