Judge

I'm NOT a mechanic and am forced to rely on what I'm told by people who are supposed to know what they are talking about. In this form I have read many reasons why my 98 Cherokee is losing oil pressure when the engine warms up. These range from the pressure gauge malfunctioning, blown head gasket, cracked head, to the engine is shot. The mechanics I've talked to face to face are telling me the oil pressure is not happening because of the above issues or a bad oil pump, but it is due to either poor maintenance, or a previous blown head gasket / cracked head that was not fixed before damage was done to the rest of the engine. Whatever the cause, the engine is shot and needs to be rebuilt or replaced. This, of course, is expensive but it is also expensive to replace a head. I don’t want to spend a load of money on replacing parts that won't cure the pressure problem, when I can spend a couple hundred dollars more for a yard engine in good condition. I know the folks on this form have a lot of Cherokee specific knowledge, and I would like to hear from some opinions on the advice I am receiving from the mechanics. By the way, the pressure gauge is new and reading accurately.

razor02097

How low of an oil pressure are you talking? Some people think 20PSI @ idle is low...

Judge

It will go down to 10, but usually between 10 & 20. It has not dropped to 0, or gotten to where a warning light will activate.

Judge

Another thing. The vehicle feels strong, and there are no unusual or worrisome noises, knocks or vibrations.

BuckB91XJ

I would personally inspect the engine myself and check for any visible cracks or oil leaking on the outside of the engine. Then, I would do a compression test, check what the spark plugs look like and check for oil in the coolant/coolant in the oil to see what's going on inside the engine. Is the engine blowing blue smoke when it runs? Is the engine actually using a lot of oil? these are all things you can do to see if the engine is damaged or worn out. If compression is good and the plugs and coolant are clean, I would go with thinking the oil pump might just be bad. Cracks in the head or block, oil in coolant/coolant in oil, exhaust blowing blue smoke, engine using eccessive oil, engine running hot, poor oil pressure are all smyptoms of a worn out engine and my recommendation to you would be to find a low mileage junkyard engine that they will give you a warranty on. That would be your least expensive route to get an engine in your Jeep that you can trust.

razor02097

If you have the ability to raise the engine enough to get the oil pan off you can make a much better assessment of the engine. Also you could replace the oil pump to see if you can salvage the good running engine you have.

How many miles do you have on it?

Judge

Buck, of the symptoms you listed the ones that apply to my Jeep are running hot, and the oil pressure issue. I have not done the compression check or tested the oil yet, and I'm being told that the oil pump has absolutely nothing to with the oil pressure dips. From visually inspecting the oil and coolant they both look like they are supposed to. No frothy milkshake looking oil, and no crud in the coolant, and I do not smell any coolant in the oil. I know that is not definitive, but I figured I pass on that little bit of extra info.

Judge

Razor. What would I be looking for once I had the oil pan off?

razor02097

You would look at the oil pump screen and any build up in the bottom of the pan.


Also when changing the oil cutting the oil filter open to check for metal is generally a good non-invasive assessment technique.

BuckB91XJ

I would definitely do the compression test and plug check. That is the best tool you have for seeing what's going on side the engine without having to rip the engine apart. Along with looking for the amount of compression. Take the radiator cap off and look for bubbles when you pump each cylinder up. The running hot thing is typical blown head gasket symptom but, you usually have the coolant and oil mixing, too. I had a rig that was running hot and losing compression in cylinders 2 and 3. The head gasket had actually blown between the two cylinders. You never said if the engine was burning oil or not (blue smoke, having to add oil a lot)? this will tell you if you just have tired rings and valve seals....That means new engine time.

Judge

Buck, no blue smoke or burning of oil. It is just the heat and pressure.

Judge

So if I'm reading Razor and Buck right, you are both telling me that the low pressure is not exclusively due to a shot engine and that a head gasket, head, or oil pump could be causing the problem. The mechanics specifically told me those issues would not be the cause of the pressure problem. I hope that there advice is due to something other than trying milk as many dollars from me as possible.

freegdr

have you check it with a mechanical gauge ,what weight oil are you running,what do you mean by because of the heat?

Judge

yes, and 10w40.

BuckB91XJ

Any mechanic who tells you that a bad oil pump can't cause fluctuating or low oil pressure should probably not be trusted. Do you suppose that he also thinks that a bad fuel/water pump can't cause fluating/low fuel/water flow?? I believe it is called an Oil Pump because it controls the pumping/flow of the oil in your engine. What a knotthead...

Sounds like he wants to make a bunch of money off of you in labor costs by convincing you that a rebuild is needed.