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Oil pressure and loss of antifreeze

I own a 2001 Jeep grand cherokee with 95000 miles on it. The oil pressure is fine on startup. When the engine warms up, the oil pressure will drop when slowing down or stopped. When I rev the engine the pressure slowly increases. Antifreeze needs to be added regularly. There is no external leaking. The oil pump has been replaced for a hefty $600. This did not help. Please help me to solve this issue before I sink my life savings into this vehicle. Thank you James Cousino

How much does the oil pressure drop? What is the pressure at start-up? Without an external leak, it sounds like a head gasket. Failure to replace it can result in more serious damage.

That oil pump replacement sounds like it was likely a dealer repair. I suggest you find a good local INDEPENDENT mechanic. That can greatly reduce you future repair cost.

I agree that the coolant loss sounds suspiciously like a headgasket. There are a few simple checks that can confirm this or rule it out. Probably the most definitive is a pressure leakdown test. Using the spark plug hole, each cylinder is filled with compressed air and its ability to hold that air is checked with a gage. If the headgasket is breeched, the air will leak into the water jacket (the coolant).

Oil pressure is really pretty basic. The pump forces the oil through spaces between the wear surfaces. If the engine is idling too low, or if the spaces between the wear surfaces grow too big, the pressure will drop. Oil pumps are simple interlocked impellars under low loads that spend their lives bathed in constantly flowing fresh oil. They really don’t wear out often…if ever.

Eight years young with 95,000 miles? What type of mileage? All stop & go? Towing? Plowing?

My oil pressure cold start-up is around 40. After engine warm-up,it drops to around 2. My check-gauges light then comes on. I’ve changed my oil sending unit, thinking this would solve the problem. No such luck. Couldn’t be that cheap.

This really sounds like a worn engine, with the bearing surfaces expanding with heat so the oil pressure drops. The loss of coolant could easily be a head gasket or a cracked head or block, or maybe a bad radiator cap that doesn’t keep the system pressurized.

A 2001 Grand Cherokee is a vehicle that has very little market value except as a trade during the cash for clunkers deal. I wouldn’t spend much on it, but you might be able to get a good replacement engine from a junk yard (recycler) because these vehicles do get destroyed by roll overs and crashes quite a lot. An independent mechanic can help you make this decision.

I suspect you have a cracked head between the 3rd and 4th cylinder. It’s very easy to check just warm up the engine, shut if off after warming and unscrew the oil fill cap. Take a flash light look straight down and most likely you will see coolant seeping from a crack in the cylinder head. If your pressure is as low as you say it’s only a matter of time before you lose the engine. The reason I know this is because I had the exact same problem and it was found as mentioned.
From what I have gathered this is a common problem with certain heads manufactured between 99-01. Good luck.

Has the engine oil been inspected to see if it’s being diluted with coolant? If it is diluted, this means the engine is gone or going because coolant is a poor lubricant and diluted oil will cause the crankshaft bearings to do what is called “wash out”.

I think you were had a bit on the oil pump. Oil pumps are the one thing that will generally never wear out. The oil pump is also the first engine part to receive oil so the shop is saying that the first thing in line is worn out and everything else after it is fine?

An oil pump replacement is a misguided attempt to cure the problem at your expense and if the shop is going to the trouble of swapping the oil pump what should have been done is to remove a few bearing caps and inspect the crankshaft bearings while the pan is off. This inspection (only a few minutes) could have saved a lot of grief and expense; assuming this is a 6 cylinder.
If an 8 cylinder I think this engine uses an external oil pump and in this case the pan should have been dropped and bearings inspected before replacing an obviously good oil pump.