1997 Suburban Low Oil Pressure!

[ZLevine]

Hello there!

About 6 months ago, I bought a 1997 Chevrolet Suburban 1500 2WD with the 5.7L V8. The truck has 150K miles on it. I've been very happy with it for the most part, but recently I've been having an oil pressure problem.

The oil pressure gauge on the dash reads low. It will start off around 40-45PSI when the engine is cold, and as I drive it will drop (usually to 20PSI), and will not go any higher than that. After driving for a long time, it drops to 0, particularly when I stop.

When I change the oil (which I do often), I can only drain about 3 quarts (it takes about 5), so I don't think that much should burn off normally. No sign of leaks anywhere.

There's a knocking noise every time I start the engine, which I think is related. After I change my oil, the knocking noise disappears for a few days until the oil pressure gets low again, and then the noise comes back again and gets worse.

I checked my PCV valve and it rattled, but I changed it anyways. No luck. I'm afraid to drive her with such low oil pressure. Any thoughts?

Thanks,
Zach

[capriceowns]

its not uncommon for a high mileagae engine like yours to burn oil.

only remedy is to have the cylinder heads rebuilt, but it could also be sneaking past the rings.

I use a high mileage oil, I know it doesnt actually help "renew" valve seals, but for some reason it burns off less for me, then regular oil. You might want to give that a try.

all you can do now, is check the oil when ever the gauge acts funny, and add some as needed.

[ZLevine]

Originally Posted by capriceowns

its not uncommon for a high mileagae engine like yours to burn oil.

only remedy is to have the cylinder heads rebuilt, but it could also be sneaking past the rings.

I use a high mileage oil, I know it doesnt actually help "renew" valve seals, but for some reason it burns off less for me, then regular oil. You might want to give that a try.

all you can do now, is check the oil when ever the gauge acts funny, and add some as needed.

Thanks for the prompt response! I don't think it's that too much oil is being burned...now just days after changing the oil, it starts knocking again and the oil pressure level drops. I've read some other posts on the forum here about similar problems, and other issues seemed to be at hand.

Does anybody else have any ideas?

[mr moose]

sounds like you may have bearing isssues . if your not leaking the oil you must be burning it ? two quarts is alot to be just missing . you could do a leak down on each cylender to check the condition of the rings . you may also have a lifter issue a bad lifter will knock at start up and could cause a low oil pressure condition . you can pull the valve covers and check for collapsed lifter . you may need to pull the pan to inspect further . sound like its time for a re build. good luck.

[horse482]

Letting your oil get as low as you stated will cause both problems, as well as major problems. Between oil changes check your oil level often and keep it topped off. What weight of oil are you running? You may want to try a thicker oil, as motors get older the tolerances are not as tight and allow more oil to pass where it was not inteded.

[ZLevine]

I was using 10/30 (even though the cap states 5/30). I haven't tried the high mileage stuff yet though. I didn't think that would work much differently.

Thanks for the suggestions I'm going to work on it today and see what I can find.

[rhandwor]

I would drop the pan and mike a rod bearing. If you talk to a machinist at a good machine shop they make slightly oversized bearings. This is a job you will have to do yourself as a garage doesn't like to do this. A gasket and bearings should be under a $100.00. The machine shop will sell you both. He will want a reading on all rods for a proper recommendation. Ceck it on two sides to make sure it is round.
20W50 oil might help you out a little if it is warm where you live. Some go to 40W racing oil.
Your nursing a sick engine.
I got stuck one time the machine shop gave me .001 bearings instead of 0.10 bearings as the crank was turned and I didn't check. Using a tool I had to pressure the system before start up I could only get 10psi instead of 40psi. I had to tear down the engine and start over. I could have trashed the crank if I didn't pre test.

[ZLevine]

Originally Posted by rhandwor

I would drop the pan and mike a rod bearing. If you talk to a machinist at a good machine shop they make slightly oversized bearings. This is a job you will have to do yourself as a garage doesn't like to do this. A gasket and bearings should be under a $100.00. The machine shop will sell you both. He will want a reading on all rods for a proper recommendation. Ceck it on two sides to make sure it is round.
20W50 oil might help you out a little if it is warm where you live. Some go to 40W racing oil.
Your nursing a sick engine.
I got stuck one time the machine shop gave me .001 bearings instead of 0.10 bearings as the crank was turned and I didn't check. Using a tool I had to pressure the system before start up I could only get 10psi instead of 40psi. I had to tear down the engine and start over. I could have trashed the crank if I didn't pre test.

Thanks for the reply. I live in a warm climate (South Florida), so using a thicker oil should work well. I'm going to try dropping the pan and seeing if there are any metal shavings in it; that might be the next clue.