thatXJguy

Hey guys.

I recently replaced my rod bearings in my 4.0L with some brand new standard size bearings. I had a terrible rod knock for about a year and it got so bad that I replaced the rod bearings.

For some time, the engine was very, very quiet.

Slowly, but surely, about 2000-3000 miles later, the engine is starting to come back with that knock. It's very slight. Nowhere near as loud as it was before I replaced the bearings.

I didn't replace the main bearings, or the camshaft bearings. At that point, I might as replace the engine entirely or rebuild it.

So here's my dilemma. My oil pressure has really been acting strange lately. My oil pressure has always been about 25 PSI or higher at a warm, 210º idle. That has always been the norm for my Jeep. Just recently, my oil pressure meter has been dipping around the 11-13 PSI mark at a warm idle. It's never done this before. So you can probably tell while I'm concerned a little.




The owner's manual says that 13 PSI is the minimum that this engine would be allowed to operate at. Anything lower, and we have a problem. I'm not getting nay check gauges lights, and I'm not getting any straight noises that my Jeep hasn't already made since the beginning of time.

I am running 10w30 Shell Rotella oil with a Mopar oil filter. I am also using an STP additive for ZDDP (zinc) for the flat tappet lifters. The miles on my current oil are about 1.5k (1.5 months).

So opinions guys – what the heck is going on here?

thatXJguy

I forgot to add. When I press the gas pedal while driving, the oil pressure does climb, so I do have oil pressure. While driving, the pressure can be anywhere from 35 to 60 PSI, depending on the speed and RPMs.

andrewmp6

Have you hooked up a oil pressure gauge to the engine to see if the dash gauge is reading true?Factory gauges are allowed to be off by 20%.

thatXJguy

Yes, it's accurate.

shortluck45

I am not a engine or tech guru but a friend of mines dad works at a Chrysler Dealership as a mechanic and he told me that as long as oil pressure is higher than 7 psi is fine. My XJ runs like that all the time. Just replaced the head and all lifters as well as a new oil pump and all seals and still does the same. I have the same little knock you are talking about. My mechanic (aka brother in law) told me it was nothing serious unless it got worse. Something about the pistons having a little ware and when at idle they wiggle a little. I may have interpreted what he said wrong but mine does the same and gives me no issues. Is not using oil and power is stable. I doubt I helped any but wanted to tell you that mine sounds no different than yours.

salad

Change the oil and filter yet? Only 2000 miles I'd rule out the obvious.

BTW no need to add any ZDDP to a diesel oil like Rotella unless you're following cam break-in procedures.

thatXJguy

I used break-in additive for the first 1000 miles after I replaced the bearings, then I changed the oil. The oil I'm running now has about 1,500 miles on it and it's pretty clean-looking.

thatXJguy

So what you're referring to is piston slap? I don't have that, I just had a rod knock. But 7 PSI huh?

cruiser54

Any pics of the old rod bearings?