Ok, jeep is at the dealership due to low oil pressure when hot. First thing I did was verify the low readings with a mechanical gauge. The dash readings are accurate. less than 5 psi at idle and 15-20 while driving. Dealership is currently diagnosing the problem and have tried a new oil pump which did not work, inspected the bearings which they said were fine, changed the gauge cluster to see if that was the culprit (of course not because I checked the readings with a mech gauge, but whatever) and changed the sending unit.. what else could this possibly be??
bad cam bearings/bad cam?.. wrong oil pump? what oil... 0w 30 or 5w 30 synthetic causes low pressure.
Could also be from a leaking oil pickup tube or screen that is allowing air into the oil stream of the pump thus reducing oil pressure. Is there a way to test oil pressure output at the pump or before the filter...oil gallery test plug like Chevy engines? What year and mileage on the vehicle?
What is the oil pressure reading at idle. as long as it is not dropping below 15-20 psi it is fine. the oil pressure is going to go up the higher the engine raps. A good rule of thumb is as long as you have 10 lbs psi for every 1000 rpm's then you are in good shape. And if you are going to go ahead and change the bearings you may as well rebuild the motor because it is all ready half way apart. If the oil pressure is below 15 at idle then yes you need to fix that. The most common cause of this would be cam bearings. You can replace the oil pump with a high volume pump to maybe help with the problem. You can un thick oil in the car. In the summer run 25-50 and run 10-30 in the winter. DO NOT RUN the 20-50 in the winter time could cause a lot of damage. Does the car make any kind of a knocking or ticking noise? Do you keep the oil changed regularly?
A four stroke engine such as yours has pressure lubrication. The oil pump picks up oil from the sump, sends it through the filter, and than to the engine. Pressure depends on fluid pushed through a restriction. Do NOT drive your vehicle with low oil pressure, or you will do permanent damage if you were planning on a rebuild. Even if you use the incorrect oil weight, 5psi at idle and 15-20psi while driving has nothing to do with it. Oil is not getting pressurzed because of either the oil pump, oil pump pressure-relief malfunction, oil leaks at main bearings, connecting rod bearings, etc... If they changed the pump and gauge and you verified with a mechanical gauge that you have insufficient oil pressure, the engine has to be disassembled and inspected. Bearing gaps have to be measured with micrometers, calipers, plastigauge etc. I doubt that the dealership will perform this. If you're under warranty, perhaps you will get a new engine. If not, don't worry. I assume you have the 4.0L I6 which is very common. I was planning a rebuild once but found out that long-block engines can be had at wreckers for about $800 with super low mileage. Good Luck.
