squirrelybird

The oil pressure gauge has not worked since I bought my car...actually it seems like it works sometimes. Anyways, I just cleaned the sending unit/sensor thing (it had oil in it?)and it the gauge seemed to work--cool, right? Nope. At first it stayed steady, but I was watching it later and the needle would drop at idle and rise with throttle. I seem to remeber that to be a very bad thing...what does this mean?

JakeJr

Oil pressure changes with RPMs. At idle it should be 20/25 psi. As RPMs increase, so should the oil pressure.
Anything aboe 10 psi at hot idle is okay,

10 psi for each 1000 rpms is a good rule of thumb.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

RB83L69

Jake's "rule of thumb" is an excellent one. It describes the engine's requirements for survival.

These cars usually do about 20-25 idling and 50-55 cruising. It is normal for it to fluctuate between these values. Above 2000 or so it should be 50ish, below that it drops with RPM.

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"So many Mustangs, so little time..."
ICON Motorsports

squirrelybird

I'll check tomorrow, but it seems like at idle it was dropping to nothing. So i'm probably okay? I thought i had heard it could be a blown gasket or something.
thanks guys

ploegi

GM had some serious issues with faulty oil pressure sending units as well. If your gauge is very "bouncy", (won't give a stable reading), or, just drops to nothing at idle, First, check your pressure with a mechanical guage, screw it in where the sensor goes, if you have good pressure at idle, replace the sensor. End of problem.....

Have fun.

Joseph Andres

iTrader: (6)

I agree with what all of you have said. There are also a few other things to check for. If you have changed your oil to a lighter weight, eg. form 10W-30 to 0W-30 or 10W-40 to 5W-30, that will give you a lower reading at idle especially after the motor has been warmed up.

It may also be a faulty sending unit, like ploegi said check with a mechanical guage first to make sure.

Another thing that may cause a low pressure reading is a faulty pick up screen in the oil pan. These have been KNOWN to fall off of the oil pump on all GM V-8's. They just seem to work their way off. One way to check is the next time you do your oil change, check to see if the pick up screen is laying at the bottom of the pan. Look through the drain plug hole with a flashlight to check. The pick up looks like a round plate with a screen on it and a bent tube coming out. If this is the case than that is the reason of having a low or no oil pressure at idle. The screen is not sitting in the oil for the pump to pick up. This is very noticeable while driving. When you come to a stop a the oil goes towards the front of the pan and starves the oil pump for oil, causing it to take in air, resulting in no oil pressure. When the oil comes back after the stop, the pressure will go back up but only minimally. When you drive along again the oil shifts to the rear of the pan, drowning the oil pump in oil, resulting in normal readings again.

The way to fix this is to remove the oil pan a and drill and tap a hole in the oil pump to where the pick up tube goes in. Put the pickup back in the pump and put a screw in the tapped hole to keep the tube tightly in place. Problem solved. Also tilt the pick up screen slightly downward towards the bottom of the pan.

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1988 GTA 5.7L TPI Auto
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