I was wondering about the oil pressure of my 1991 z28 305. When i start the motor, it runs fine and everything, but when i look at the gauge it reads rather low oil pressure almost to the red line. when i rev the motor a little it moves up, but just a little bit. Do i need a new oil pump? or do these motors just have low oil pressure to begin with?

 

Sounds like a bad sending unit. How many miles are on it?

 

69xxx miles are on it

 

Is this a sudden change from higher readings, or has it always been that way and for how long? How long since you changed the oil, and what weight do you use? Not being nosy, but more details might help some. You say when it revs it goes up a little bit. How many pounds of pressure is that, at first and after revving?

 

Heres whats up. Its about time to change the oil (3000 miles). I used 5-w30. The pressure from what i remember has always been kinda low, but not this low. When i start the car, its below the half way mark behind 30. when i rev it it moves close to the tick. The gauge is nearly on the redline. i cant really say how much pressure its reading due to the fact im going by the gauge. hope that helps

 

generally speakin, a sbc chevy that is stock only needs 7 psi oil pressure per 800 rpm on a motor that isnt driven hard. but id try the oil change and a sending unit, could be a dirty pick up screen on the oil pump.but with ur milage it should be readin higher than that

 

i appreciate it. thanks alot

 

Yep, more likely the sending unit than the oil pump, but see how it turns out

 

I fixed an engine like that. When first started up it had good oil pressure. Once the oil got hot, the pressure dropped to almost zero and reving it up, the pressure would increase slightly.

Turned out the engine had bad cam bearings.

When diagnosing low oil pressure, the first thing you do is mount a mechanical gauge to confirm if the pressure really is low or not. If it isn't, then you can move on to determining if you have a bad sending unit or gauge. If the mechanical gauge says the pressure is still low, then you start determining why. Very rarely will a pump produce low pressure like that unless it's had a lot of dirt go through it to score up the surfaces.

Higher pressures are always nice but a minimum of 10 psi per 1000 rpm is safe. Anything less than that and you risk starving bearings of oil.