no oil pressure please help!!

devin16 · May 15, 2005

it is a 1989 gmc regular cab stepside with the 5.7l 4x4. i just bought and when i start the vehical the pressure is at 200 and then after a while it dropes to zero and i dont no y can some one please shed some light on this.

thank you!

bronyaur · May 15, 2005

How many miles are on it? Assuming there's enough oil in the system, I would be inclined to think that the main and rod bearings are shot. When the engine is cold the pressure is up because the oil is more viscous (thicker). But, when the oil heats up it becomes less viscous and therefore flows through the gaps in the bearings more easily, reducing pressure.

Friz · May 15, 2005

I agree with bronyaur.

Is it really at 0 or just real low?

You need 10psi of oil pressure for every 1000rpm

mcreyaufmiller · May 15, 2005

check the oil, make sure there is some in there.

May 15, 2005

I agree....if it has oil, you may have spun a bearing.

Mr. Smith · May 15, 2005

Put a real mechanical gauge on there to check that it isn't the sender or the truck gauge. No sense in blaming bearings or pump unless you can verify the accuracy of the readings with the dash instruments.

My .02

mmmikkke · May 15, 2005

Your oil pressure gage goes up to 200?????

Cool Zr2 · May 16, 2005

I know this guy who had his pickup tube fall off his oil pump. Might want to look into that.

devin16 · May 16, 2005

it has 300 000kms and i just changed oil and its full. i was going to check to see if the guage was working but i couldnt find the oil pressure sensor to use an external one to check the psi. dose anyone know where the sensor is on the 5.7 its a 1989.

Mr. Smith · May 16, 2005

look to the left of the distributer, you should see a sending unit.

it has 300 000kms and i just changed oil and its full. i was going to check to see if the guage was working but i couldnt find the oil pressure sensor to use an external one to check the psi. dose anyone know where the sensor is on the 5.7 its a 1989.

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devin16 · May 17, 2005

k thanks. i did a compresion test on all of the cylenders and everything is up to par so i have no idea what the problem is. i will check th preasure with an external gauge tommorow. what outher posibilitys are there if the preasure is right?

Mr. Smith · May 17, 2005

If the mechanical gauge shows good pressure, look into a new sending unit or a faulty instument cluster gauge.

k thanks. i did a compresion test on all of the cylenders and everything is up to par so i have no idea what the problem is. i will check th preasure with an external gauge tommorow. what outher posibilitys are there if the preasure is right?

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