Oil Pressure Issue on my old GMC.
 

I'm quite good with cars, and this has me stumped, but I want to know what's wrong before it goes by the wayside.

This is a 1993 GMC Sierra C2500 with a 4.3L. My father ordered it brand new, and it was given to me in 2005. Well, it now has 254K, and I bought another 1993 GMC sierra to replace it. THIS time, it is fully loaded, and has a V8!

What caused me to do this, was the lack of maintenance on it preceding me, had finally begun to catch up with it. I'd fix one thing, knowing that 4 other things are about to fail.


It's on it's second engine, a JASPER reman, with 125K on it now. In December, it blew a head gasket. Drove it home that last mile, and parked it. It took me nearly three months to fix it, because I had my Town Car to drive, and it was 30*, plus 20 MPH wind chills, = me not wanting to stay outside for extended period of time to fix it.

In February, I got ti running. All was well, except for the oil pressure.

It used to be 25 at idle when warm, and 45 or so while driving.

Well, at it's most extreme, it has /does dropped/drop as low as 10 PSI at idle, and 28 while driving.

It doesn't knock, or make any odd noises, which leads me to believe I did not spin a bearing or anything, but when you start it up initially, OP is 45 PSI at idle. Then, as it warms up OP drops...to around 15 or so, and stays there, until you idle up the motor. It maxes out at 30 @2200 RPM's when it's supposed to be 45 PSI.

It makes no odd noises, or anything. Sounds like a normal motor. Any ideas? Usually, when the oil pump goes, it just goes. I see no signs of it on it's way out, I really am stumped here.


Like I said, it was replaced with the truck I talk about now, but, I still have the old one, and want to figure out what's wrong before I let it go.
I'm quite good with cars, and this has me stumped, but I want to know what's wrong before it goes by the wayside.

That is actually normal on a higher mileage motor. We used to have an old wrecker that had 10 PSI max and it ran for years like that. Your oil pump may be getting weak, but more than likely the ole motor is just getting tired. Getting it hot enough to blow a head gasket may have put some strain on other components.

Well see ,thats the thing. It blew the gasket about 3 minutes after initial start up. Engine was still fairly cold.

Normally, I'd agree with you on the "it's just getting old thing" but it was fine before the gasket blew, and not after.

i have a93 gmc as well with low oil pressure i also had a bad radiator when i changed the rad i removed the external oil cooler and oil psi went threw the roof after a few weeks and a few oil changes it returned to normal i also added a bottle of lucas that may have helped spike it at first oh by the way 283000 ive just recently replaced the cam only to find lots of gunk in the intake valley ......must have been a penzoil user