I usually only drive my car for about a 30 min at a time during my commute but today i probably drove it for 2 hours of city driving so I was idleing at lights and whatnot. Towards the end of my drive my oil pressure was down at the bottom on the guage (stock guage). During most of the drive it was in the middle of the guage. My motor is a 74 350 and was rebuilt about 3000 miles ago. I know my motor has a slow leak from the rear main seal and from one valve cover. Could this be the cause of such a rapid decrease in oil pressure or is there something else. I dont think it should be the oil pump because that was new with the rebuilt motor. Any help would be greatly appreciated because this is really bothering me after I paid for the motor.

Thanks,

Matt

 

Mechanical pressure gauge first. Go from there.

 

Alright I do have a mechanical one that I will try out. Are the stock Z 28 ones known for being crappy. My car has about 190 K on it.

 

notorious for being crappy

 

As oil warms up (notice I said oil, not engine) the pressure will decrease.

As said, hook up a mechanical guage and go from there.

 

Thats what I'll do and I will get back to you guys hopefully that is it. Can a slow leak cause a pressure drop like that?

 

Consider this: oil pressure is made by the resistance to flow. The oil pump does not make the pressure. It merely draws the oil from the pan, via the pickup tube and pushes it into the block. Bearing clearances, small oil passages, things like that create oil pressure. The only things that could really create a loss of oil pressure are increases in the bearing clearances, etc, which would be an indication of parts that are worn, or, the pump not delivering the oil volume it should, which would be something like a clogged oil pickup.