Oil Pressure Problem

[jamilz28]

Hey there,

Just signed up, first time posting. Thanks in advance for the help!

I have an '81 z28. It's got a 350, Super T10 4 Speed, and it's mostly stock.

When I first purchased the car 5 years ago, my oil pressure on start up was 70-75 psi and 35-40 at warm idle. It never went below 30 psi. Ran like a champ.

Now, oil pressure is at 55-60 psi at start up and once its warm it will gradually continue to drop to well below 20. The longer I drive the lower the oil pressure will get to the point of stalling if I dont keep the rpms up.

I know the basics, but not enough to diagnose the problem myself. I've had mechanics tell me that my main bearing is going and that I should just get a new engine. Others have said it could be the crank bearing.

I've also been told I should just put straight 40 weight oil in it and it will bring the oil pressure up even with the possible increased clearance on the bearings.

Lastly, some have said I need to swap in a high performance oil pump to compensate for the low oil pressure.

I'm not really sure what to do with all this advice. Has anyone else had this problem and fixed it? What do these symptoms sound like to you guys?

I only drive it in the summer and I haven't heard any knocking noises or anything yet. Currently running 10w30 on a shop's recommendation.

 

[djorgensen3]

I would definitely STOP DRIVING IT UNTIL IT STALLS. Whatever is wrong in there is just getting way worse. You should probably pull the pan and check the condition of the bearings and pump at a minimum.

 

[jamilz28]

I would definitely STOP DRIVING IT UNTIL IT STALLS. Whatever is wrong in there is just getting way worse. You should probably pull the pan and check the condition of the bearings and pump at a minimum.

Oh, I don't drive it till it stalls. That just happened the one time. If I do take it out it's only a short drive and I keep rpms up towards the end of the drive to keep oil pressure up.

 

[djorgensen3]

Okay gotcha. I would probably take a look in the bottom end though.

 

[Twisted_Metal]

Pull the oil filter and cut it open.
It there's glitter in the pleats of the filter.. You're losing metal somewhere.

What you're experiencing are symptoms of an eventual catastrophic failure somewhere down the road.

If it was my car.... I would pull the engine and tear it down/rebuild it before it grenades, or... Replace it.

Personally, I would lean towards replacing it with a new crate engine (with a warranty) before I would deal with machine shops if it was beyond my skills to rebuild it. Depending upon what was found upon tearing it down.

If it's the factory engine and you're not looking for any more performance, the 250 HP 350 CI crate engine from your GM dealer will be pretty much the same as what you have and will cost around $2k by the time you buy gaskets etc.

 

[1980RS]

Test it with another gauge first to make sure it's not in error, then check the pump and bearings.

 

[jamilz28]

Test it with another gauge first to make sure it's not in error, then check the pump and bearings.

I can try testing it with another gauge but I dont understand how it could possibly be a faulty gauge when the engine actually reacts to the low oil pressure by dropping in rpm at idle and eventually sputtering to a stall.

 

[jamilz28]

Pull the oil filter and cut it open.
It there's glitter in the pleats of the filter.. You're losing metal somewhere.

What you're experiencing are symptoms of an eventual catastrophic failure somewhere down the road.

If it was my car.... I would pull the engine and tear it down/rebuild it before it grenades, or... Replace it.

Personally, I would lean towards replacing it with a new crate engine (with a warranty) before I would deal with machine shops if it was beyond my skills to rebuild it. Depending upon what was found upon tearing it down.

If it's the factory engine and you're not looking for any more performance, the 250 HP 350 CI crate engine from your GM dealer will be pretty much the same as what you have and will cost around $2k by the time you buy gaskets etc.

Ok, I'll pull the oil filter and take a look. Seems like engine replacement is where I'm headed. Maybe now is a good opportunity to try learning to build a 350 myself.

 

[1980RS]

I can try testing it with another gauge but I dont understand how it could possibly be a faulty gauge when the engine actually reacts to the low oil pressure by dropping in rpm at idle and eventually sputtering to a stall.

Had a 396 that went to 0 oil pressure, changed a gauge and it was fine with that one. Funny thing, the bad one was an Auto Meter oil gauge. save you extra work by doing this step if it shows bad.

 

[jamilz28]

Had a 396 that went to 0 oil pressure, changed a gauge and it was fine with that one. Funny thing, the bad one was an Auto Meter oil gauge. save you extra work by doing this step if it shows bad.

Ok I'll check it out.