A friend at work said that he had accidently over filled his engine with an extra quart of oil. He did not drive it very far before he noticed that at idle the engine only had a 6 psi pressure. Before it would have 40 psi at idle . As the rpm's raised the oil pressure would raise to a normal pressure. He removed the extra oil but so far the oil pressure is still down to around 6 psi at idle. There is no lifter ticking or anything else. The engine is out of a mustang and has themustang type oil pan on it. What could of caused the pressure to drop down?

 

Which Mustang engine is this? 4 or 6 or 8; early or late?

 

It is the 302 5.0 L V8. Don't know exact year but around late 80 early 90's was originally a EFI motor.

 

That engine should be able to handle an extra quart for a short time. The most likely problem from a severe overfill is that there is not sufficient air volume to and the pressure can blow out the seals. It is hard to see this happening at only one extra quart (~3/4") of oil.

I'll admit it I am stumped. All I can say is coincidence, but that does not explain anything. (If your friend had driven without any oil for a while, this would be easier to understand.)

OK, I'll take a guess: The oil pressure relief valve plunger could be stuck, but I do not see how an extra quart of oil could have caused it. Is the 6-psi at hot idle or cold idle?

 

I believe it stays at 6 psi at cold and hot. not sure but would have to ask to make sure. The oil pan had been modified a little. He put the motor in a Miata and had to remove some of the center section to clear the cross member under the car.

 

Perhaps a thinner grade of oil than what was in it before?

 

My friend told me today he figured out what hppened. Not only had he mistakeingly added a extra quart but his fuel was leaking into the engine. Once he got the oil changed and fuel problem resolved the oil pressure went back to normal. Thanks for all the suggestions