Jeff H

New guy, old question?
Searched for this and couldn't find anyone asking the same. Got sidetracked a lot reading unrelated stuff and found that a lot of things my '98 Cherokee Sport does is not unusual.

Background - I have put over 200k miles of the 243k miles on my odometer on my '98 XJ (4.0L) all by myself. Original engine tick evolved to a knock and I pulled it at 228k to rebuild before I completely ruined it. Knowing it would take a while, I put in a '96 engine with 92k on it. At 228k, the old engine would hold 40 psi at idle and 50 psi at 2k rpm.
The "new" engine holds 10 psi at idle and 40 psi at 2k rpm - most of the time. Running the new engine at 3k rpm sounds like pouring a bucket of marbles onto a glass coffee table.

No big deal, since I plan to rebuild the other, BUT I test-drove an '01 with 74k miles on it today and it it started at 40 psi while warming up, but dropped to 10 psi after warmed up. Temp's running around 210F. The '01 with 74k miles sounded like a gigantic sewing machine after having run at temp for 20 minutes. It was a very nice vehicle other than that.

Since I am on a quest to find another '98 through '01 before they are all gone or only good as "project vehicles," I was curious if there was anything unusual about the 4.0 that lends itself to low oil pressure issues other than good ol' fashion bearing wear?

Thanks.

Rock Toy

Some people run the 5-20 in there cars and that is a problem because the 4.0 isn't built to use that thin of oil. I'm not saying that is why the pressure starts off at 40 and after warming up drops to 10. Just that it could be possible. A guy at the speed lube tried to talk my wife into using 5-20 in her super charged 3.8 liter Buick because that was the newest thing, she was smarter than that though.

Jeff H

Good for her!

Fortunately, I do my own changes and have always used 10W30, as spec'd, in the '98. I wondered if it was different for the '96 transplant and tried 10W30 on the last change and it's higher initially, but drops when warmed up. Not sure that is any better tha running thinner but was curious as to what the affect would be.

COULD be this issue with the one I looked at today. Who knows what was put into it and when it was last done?? When I told the salesman what I found that scuttled the deal for me he immediately asked if I wanted to make an offer to take it as-is.

The oil was definitely overdue for changing. I was thankful they did not "service it" as they said they did. I got to see/smell the real stuff the last user had in it.

So, what was first - chicken or the egg....?
Hydraulic lifters rattling because of low oil pressure.... or
Oil pressure is low because lifters aren't pumping up?

Rock Toy

I usually do my own changes but at the time I was working about 300 miles away.
I was more or less talking about the one you said you were looking at to buy. Good luck on your decision.

UserID6095

Jeff, low oil pressure on the factory gauge is not always an end all situation. Without verifying the oil pressure via a mechanical gauge it would be tough to diagnose.

On that note, my '96 with 180k hits 60psi at cold start and drops to 40psi once warm.

Common issue for low oil pressure is the pump going out and/or poor maintenance and the crank/rod bearings are worn. IMO, Cherokee's are too common to spend money on one with what may be a bad engine. I would look around for something else.

Jeff H

Yeah, sometimes my daughter has her car done at an oil change place. I can't keep up with them all. You're right about the other Jeep though - you just don't know what someone has done to it.

Need to find a private sale. The ones I have seen on lots were pretty nasty. Made me appreciate mine a lot more.

Still looking.

Thanks.

Jeff

Jeff H

Right - gotcha. Bad oil pump is bad enough, but poor maintenance......
Been looking at (and smelling) the interiors to gauge that somewhat unscientifically. If you'll sit in filth, why would you bother with what you can't see under the hood?

Patiently looking for a decent one right now. The one I am driving will get a quart of Marvel Mystery Oil with the next changes to see if it frees up the lifters. Engine runs well, sounds good up to 3.2k rpm. I will check with a mechanical gauge too. From what I am reading as I poke around here, holding 20 PSI at idle and 40 at 2k rpm is not that uncommon.