CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Jeep loses oil pressure

2001 Jeep Grand Cherokee Laredo, replaced the oil pump with a new one and washed oil pan and replace the pump screen. after driving for about 30 minutes when at an idle/low speed the oils pressure goes low enough to set the check engine light on. The motor sound good sometime there is a little clacker, oil sending unit replaced and have installed a mechanical gauge… please help what else will cause this?

How many miles on the Jeep? Are you sure the old oil pump was bad? Oil pumps rarely go bad, so your problem(s) may have more to do with a “tired” old motor. What were the symptoms and reasons behind replacing the original oil pump?

205,000… it was gunked up and the pan had about an inch of matter in it and the screen was clogged… any suggestions ?

Have oil changes been done on schedule all along?

just bought this summer but only driven it about 75 miles, so I do not know…

Based on the mileage and the crud in the pan, this vehicle had likely seen very few oil changes, and it’s likely that the bearings, etc., are so worn that the pump (likely also worn) could not build up any pressure. An engine with that many miles and with good care should not have any sludge in the pan.

My vote is with Docnick and something to keep in mind is that an oil pump seldom ever goes bad or worn out. I’ve never seen a faulty one in all of my years although I have seen and heard of a number of them being replaced in a misguided effort to cure a worn out engine.

The oil pump is the first thing on the engine that receives oil from the pan. If the first domino in the string is worn out then it follows that everything after it is worn out even more; assuming one had a situation in which the pump was legitimately faulty.

If you drop the oil pan and remove some crankshaft bearing caps you will probably see nothing but copper showing; meaning it’s worn out.

It sounds like the poster child for the “don’t fix it if it ain’t broke” crowd. considering the condition of the oil pan I am amazed the engine lasted 200,000 miles. If the journals are not wiped out replacing the rod bearings and the center main bearings might give the engine a few thousand more miles. But then, it might not make it out of the driveway when you finish. Which engine is in the Jeep?

4.0 6cylinder

We replaced the pump because of the gunk was in it and gummy

You have a low oil pressure at idle, could be major bucks to fix it. Basic fix is get a rebuilt engine or deal with it until you need a rebuilt engine.

you need an oil pressure switch/oil pressure sensor.

that is all.

The oil sensor has been replaced and a mechanical gauge was also installed to make sure the measurement is correct. Then after that was done, the next step (since it happened again) was, we removed the oil pan that’s when we found all the gunk in the pan and screen. we first rebuilt the oil pump because of the gummy build-up (happened again oil pressure goes to zero). Then we replaced it (oil pump)… drove fine for two days then at the end of the second day the oil pressure went to zero at idle… again.

Oh ya, forgot we checked for blow-by, at the valve cover none, the exhaust shows no sign of oil blow-by normal look no gray smoke of any kind… the only time I here any clacking is at start-up for about 15-30 secs. I have a feeling it may be the bearings for the crank and/or cam? what do you all think… Compression test showed good (forgot the readings) on all cylinders…

Had a similar issue with an '89 jeep with the same 4.0 engine. I would pull the pan again and use plasti-guage to check the main bearings. If they are way off or copper is showing, Jeep used to sell bearings that are .001 and .002 over sized, that you can use to make the tolerances tighter. Depending on the damage to the mains, it might buy you 6 months while you save up for a crank kit or better a rebuilt. A mechanic friend also suggested using synthetic 20w-50.

Thank you all i we will check the bearings at first chance… and see if that works pricing rebuilt prices this week…

one more question on this subject. Does anyone of you all recommend Motor Honey to help, until I can have the engine rebuilt? just asking… I know we used that in really old cars that had a lot of oil issues when I was younger…

Motor Honey can help quieten an engine down and can increase oil pressure.
However, there is a potential downside to making engine oil too thick.

If the crankshaft journals and bearings are worn badly enough it’s possible for excessively thick engine oil can cause a crankshaft rod bearing (as opposed to a main bearing) to change sides; meaning that both bearing shells will be on the same side of the journal.
An engine has to be badly worn for this to happen, but it is a real possibility and something I’ve personally seen a couple of times.

When, or even if, this occurs the engine will make a lot of noise, stop running, or throw a connecting rod.

Given the situation as it exists, I would run 20/50 motor oil in it and not go any thicker. The clacking you hear upon startup is due to worn out crank bearings which shut up momentarily when oil pressure hits them.

When the oil pressure nears ZERO it no longer hits the bearings, it’s more of splashing in there among them. And if the climate is mild adding ‘stabilizers’ might help but 20W50 plus Motor Honey at temperatures below freezing can cause worse problems than it cures.