bigbadon

Not to burst your bubble but the likelihood of 2 bad filters in a row is slim to none.
I traveled down that same path when I bought my first jeep,yup,filters,oil weights,pump,bearings head check and still 4-5 psi and check gage alarm. I am a very experienced mechanic but that was my first encounter with the 4.0 engine. After much research I found this to be a common problem for that year and a few years before. That was also the same years for the cracked 0331 head issues which will destroy bearings and cause low oil pressure. BUT jeep also had the pressure problem too....non related to the head.
There have been 4.0s rebuilt by professional engine builders that have come bake with low oil pressure. There has to be an explanation but I failed to find it.

PocketsEmpty

So you're referring to strictly 2000-2001 Cherokees, correct? Those where the only years that had the 0331 head. It IS possible to have two bad filters in a row for this engine if it isn't the right kind. The 4.0 is finicky about its oil filter.

The check gauge light coming on and oil pressure dropping that much can't be normal. I have a 1998 4.0 and I hold steady at 10-12 psi at idle, and anywhere from 30-50 while driving.

bigbadon

While true Fram has had a bad reputation with filters it is still very unlikely. The 4.0 is a very basic and ancient engine and is not picky on OEM spec filters. The 4.0 oiling system is higher pressure than most cars so oil is going to get through the filter unless the filter media collapses and clogs the the filters outlet side or worse,the oil galley. BUT if this were the case the pressure would be low at cold idle!

No I did not say low oil pressure for these years was normal....I said it was a COMMON problem.
What has the greatest effect on pressure that people overlook? Worn lifter bores, bad block casting or mis alignment when oil gallies were drilled/crossdrilled. A leaking oil galley (or missing galley plug) is not an unheard problem.

RTorrez1

Not true! You can put 100 filters on and have the same problem if they are all crappy filters.

bigbadon

Where is the class action lawsuit? Has this been documented by S.A.E.?

BearBrown

Ok, I tried this today. I took off the valvoline filter which is a bosch according to a guy I called at the shop. I installed a napa gold filter (which is a wix filter according to the guy at napa). The results are still the same. Oil pressure is fine when the engine is cold and drops to zero at idle when warm.

I also tried this:

http://www.jeepforum.com/forum/f19/4...fixed-1304679/

If you dont click on the link here is what I did... I took off the oil pressure switch for the electric guage again. I took pipe cleaners and tried to clear the passage to the gauge in case there was a bottleneck of sludge or something in there. Then I put in a brass hose fitting into the threads where the switch goes and ran a hose to a drain pan from there. I started the engine and increased rpms to about 4000 for a few seconds. About a quart or little more of oil came out. I added more oil, and tried it again. Added more oil, and hooked the switch back up and took it for a drive. Same issue.

Turbo X_J

Give it a couple hundred miles of use then spend $25:

http://www.blackstone-labs.com/

bigbadon

x2 Look at the glycol level. If your experienced you can test for glycol with a blotter test and save $25. Ask around, maybe some "old school" mechanic can help you.

shackwrrr

Put 20w50 in it and if the oil pressure comes up replace the bearings. You can get to all or most of the bearings underneath and replace the rear main at the same time. If its not making any noise then the crank and rods are good.

BearBrown

I considered just sticking some heavier oil in it and seeing if that would make a difference...

But I didnt buy a 4k truck to immediately pull it all apart and have to do motor work (something I dont know how to do). I took the truck back to the guy I bought it from this evening. He has better mechanical knowledge and proper equipment to do that sort of work. We have an agreement written up and I should know more by thursday. Hopefully I'll either end up with a properly running truck or my money back.

I'll report more as this progresses. More thoughts and ideas are very welcomed still.

kennzz05

have you researched the 0331 head issue? read up on it while the truck is in the shop, did you notice if the coolant level had dropped at all while you had it? click the link to do some research on the head:

https://www.google.com/search?q=cher...hrome&ie=UTF-8

dr.zoidberg

im really happy someone else brought this up....i recently bought a 97 xj and at start up and while cold i run a solid 45 to 48 pounds of pressure....but once it gets to operating temp, 2k and above i still have 45 to 48 psi...when its at idle i drop to 15 to 18 psi......really happy to hear this is normal.

viperbabe35

X2

PocketsEmpty

Normal indeed. You're in the green!

to the OP, sorry to hear the filter wasn't the issue. However, now you can have peace of mind that you have the best filter you can get. Your 4.0 will be happy about that...but I'll agree with the others, monitor the coolant level or anything unusual with the cooling system.

I've seen a few things about this in other threads. Peace of mind might be worth the price.

Radi

Old fart trick: Pull the pan and the oil pump and apply compressed air. Sometimes you can find the source of a gross pressure loss is with a stethoscope.