Been racking my brains out researching this common problem in the 2000-01 XJ 4.0 L. It seems as if though I have a cracked head (0331) and have done something to piss the Jeep Gods off. As a result, I have very little oil pressure - a tad above 0 at idle and 20 at cruising speed. Just installed a new oil pressure sensor, same result. Installed a mechanical guage, same problem. I am thinking of replacing the oil pump, but numerous other forums (JP) said when they did this it did not work. I do not lose coolent quickly, I'd say over a 2 month time frame the reserve is empty. Jeep runs strong (real strong) with no obvious noises (slight ticking from the lifters, common trait). Jeep has just under 150,000 miles on it and doesn't seem to be on a death watch, but since it is my daily driver, what options do I have? Need some good advice as to possible rebuild, new head, new motor, etc. Any advice or anyone knows of someone who knows this Jeep, please let me know. (sorry about being so long)

I am not an expert but I have the same problem in my 91' YJ so I will share what I was told. Apparently this is a fairly common issue in these in lines as they age, and is most likely due to bearing wear in the engine. This doesn't account for any coolant loss so you may have other issues, but I was told not to worry about it. I have basically ignored it for the last 4 years or so but when I switched to rotella oil my oil pressure increased to about 10lbs at idle. I did this because I noticed my oil pressure was higher after a fresh change and wondered if a different kind of oil would help. If it is just a sloppy motor the only way to fix it is a rebuild.

Toss in a set of bearings. They are cheap and it can be done easily without pulling the engine. We had a ZJ on the lot that didn't even make a peep. After it would warm up it would lose all pressure at idle. I replaced the bearings and it was as good as new. Took me about 5 hours of taking my time and resting my arms here and there, yacking on the phone, ect.....

The ticking you are hearing is more than likely its piston slap. The inline motors have fixed lifters they can't be adjusted. Inline Jeep motors are famous for it. The low oil pressure is exactly what goose said. replace the bearings and your oil pressure will come back. The only way to fix the piston slap/ticking is to tear the motor down and rebuild the motor with new pistons and boreing the block. I would run the motor till it dies before worring about the piston slap. I have seen these motors run a long long time its just annoying to listen to.

V-8 Swap.

440 Hemi would be cool!

x2 on the bearings. Low oil pressure is typically a problem with worn rod and main bearings. Best get them done ASAP before you end up needing stuff machined.

On the piston slap... my brother's 98 seized back in November. I thought it was a bearing problem, but it ended up being the #6 piston detonating into a couple hundred pieces. Apparently around 96 Jeep went to a shorter skirt piston, causing it not to handle slap as well as the older ones.

This is what I got when I pulled the pan:

I hear y'all. I was told if you tear down the bottom end and replace the bearings, you should get the crankshaft machined to bring back into spec. IDK. Doing a lot of research in a lot of forums to diagnose problem and the best long term seems to be a reman 4.0. Ends up being cheaper for me since I have no place to tear engine apart and rebuild and a shop would be more expensive using new parts. Since it's my DD, I may have to bite the bullet and make a "new" Jeep. Motor I'm looking at has 3 year, 50,000 mile warranty and gives me peace of mind. I appreciate all the advice though.

"If you keep it in the ditches, smokey's off your britches"

Where are you at? I can replace the bearings for a few hundred bucks and the 6 will lasat forever. A reman is going to be at least 2 grand for the motor alone plus labor.