BearBrown

I just bought a 2001 jeep cherokee sport 4x4, 4.0 liter, inline 6 with 95,xxx miles on it. After driving it home, I noticed the check gauges light came on and the oil pressure gauge was reading nearly zero when I stopped. This of course didnt happen during the test drive.

Generally the issue goes like this: oil pressure seems fine when the vehicle is cold. But after the vehicle warms up and has been driven a while the oil pressure reads lower at highway speeds than when it is cold. When I come to a stop and idle after driving a while, the oil pressure drops to nearly zero and the check gauges light comes on.

Things I have tried: changed the oil today (10w30 the recommended oil weight in the manual), new oil filter and had the guys at valvoline check all other fluids. This did not fix or help the issue. The oil that I changed out was next to new and was at a good level.

Next I removed the oil switch by the oil filter (the switch looks new). Then I attached a manual gauge where the oil switch was. The manual guage confirmed that my electric gauge is correct and that my oil pressure is low. 6-8 psi at idle when warm and pressure climbs if you rev the engine and increase rpms but drops back down after you let off the gas.

So what do I do next? Should I remove the oil pan and replace the oil pump? Can anyone give me a detailed write up on how to do this? There arent any knocks or weird noises coming from the engine yet, but I dont want to ignore this and ruin my new truck.

bulrid8

That is about normal pressure for the later years. My 98 runs 38-40 psi at 2k Rpms. Drops to 8-10 at idle. I believe from 97-01 they are all like that. As long as you have no noises from oil starvation. Don't worry about it.

I freaked too, first time I seen it. My 93 runs 28 at idle, 48 at 2k rpms. But newer models run low pressure at idle

Bustedback

13psi is the minimum recommended oil pressure at idle. A new oil pump will most likely not fix the problem. Oil pumps create flow, not pressure. It's the tight clearances between the crank, rod, and cam bearings that make pressure. In other words, resistance to flow makes pressure. It wouldn't hurt to drop the pan and see if the oil pickup is clogged. The pump can't create flow if it can pick up the oil.

Radi

Previous owner happen to say anything about replacing the head at some point?

BearBrown

Nothing of the sort was mentioned.

I've been doing a bunch of reading on this and one of the things that I have seen mentioned a couple of times is the pressure relief valve spring on the oil pump getting stuck because it is grimy. Is this a possible explanation for my issues?

Radi

I'd think if the valve were stuck it'd stay stuck and you'd have low or no oil pressure hot or cold. A visual inspection of the pump, screen, etc. would be worth the time though.
Dropping oil pressure as the motor warms up is normal to a certain extent, but dropping abnormally low is often a sign of excessive bearing clearances- that's why I wondered about the head. Antifreeze in the oil can cause it and that mixing generally happens with a cracked head. The head problem gets fixed then the oil pressure problem appears.
That year, IIRC also had problems with cam bearings and low oil pressure regardless of any other issues.
If it were mine, I'd peek at the pump and pickup/screen then take a look under the valve cover and verify the rockers are getting oil at hot idle. If they are and the engine and valvetrain remains quiet, I'd not worry about it until you are ready to do a rebuild.

RTorrez1

What brand of oil filter do you have on it? A crappie filter can also give you a little lower oil pressure. When I bought my last XJ it had a fram filter on it and it had a low oil pressure reading. I changed it out and it did increase the pressure. Our 4.0 seem to like the Mopar, Wix and Napa Gold filters best.

PocketsEmpty

x2. Surprised this wasn't asked first before all that crazy talk about engine repairs.

I had the same issue with my XJ with the oil pressure dropping to near zero and hearing the awful sounds...the next day I ditched the Fram and put a Napa Gold filter on, and not an issue since.

RTorrez1

I was surprised too, That's why I had to ask. That should be one of the first questions to ask when ever someone asks about low oil pressure.

pdowty68

My oil pressure is a little jumpy at idle too. Could it be the sender?

PocketsEmpty

Verify that with a mechanical gauge....otherwise...see posts above

bigbadon

x2 Not all did but a bunch in 99 -2001 had this issue and Chrysler has never given an explanation or confessed up to it. There are a number of causes but no one I know has ever pinpointed it. Most cases get blamed on the cracked head scenario but this IS NOT always the problem. There have been countless stories of owners replacing oil pumps, bearings and even complete rebuilds and still ending up with low pressure.
You don't need pressure, you need flow. If you have oil flowing under the valve cover it will be getting everywhere else.
There are less common causes of low oil than bearings or filters....bad block casting or oil galley drilling is one. Oversize lifter bores is another.
Mine guage has read zero at idle for so long that I don't even pay any attention to it and I drive all over the place.

BearBrown

I literally had the oil changed yesterday by valvoline. I'll check and see what it is specifically. The guy I bought the jeep from had changed the oil before he sold it to me. So it has had two different filters on there already without improvement.

PocketsEmpty

They probably threw on an STP or Valvoline brand filter. I'd say ditch it and throw on a Wix, Napa Gold or Mopar as stated above, and then report back results.

RTorrez1

But what brands are you using? If they have been crappy filters such as Fram or the garbage that they put on at the oil change places that ca still be your problem. The 4.0 needs a good quality filter with a good drain back valve in it. Like I mentioned before the best for our 4.0's are Mopar, Wix and Napa Gold.