I have low oil pressure in my 4.0L. It starts at 50-60 cold, then after the engine is good and warm it drops to 20-30 driving, and 15-20 at idle.

I have put crank and rod bearings in. Also I put a new oil pump in. I am running 10W40 and thinking of going to 20W50.

I was thinking it might be the oil pressure relief valve. But I cant find any listing for it. Does anyone know where the pressure valve is on the 4.0L.

It is a 1990 JEEP CHEROKEE LOREDO 4.0L with an automatic.

Please Help...

 

higher than mine has had in the last 20,000 miles. And i cant kill mine, im secretly hoping it will pop but, no dice

 

Not sure what year you have but the recommended oil for the Cherokee is 5W-30 in cold weather and 10W-30 in Hot.

 

The pressure relief valve should be part of the oil pump. If you still have your old one take a look at it and it should be in the oil pump.