Originally Posted By: OE812
It is good to be a member of this informative forum. For the past several years I have been searching this forum. I like the years of research that has been done on engine oil and engine filters. I had no idea the site has grown like it has until today when I became a member.
BTW, do you like the 4.0L engine? Any issues with the Jeep?
I've owned two 4.0s and known a number of others who have owned them. Its one of the truly all-time great engines, and only got bad reviews when pushed to do things it wasn't meant to do (in the latter years, reviewers complained about its lack of highway passing power... duh. Its a stump-puller designed FOR offroad vehicles.) Maybe the best testament to the 4.0 design is how admiring Chrysler's lead engine designer was about it when Chrysler took over AMC's engine operations. And he made its little-brother 2.5L engine the replacement for HIS OWN Chrysler 2.5L engine in pickup trucks, as it was more suited to the heavier vehicle application than the overhead-cam aluminum-headed Chrysler 2.5 was.
The 4.0 went through a few years with some cylinder head issues from the end of 1999 through about 2001, but yours should be after the affected years. Some in that era also had excessive cam bearing clearances causing low oil pressure (but not low FLOW) my 2001 has that issue and continues to soldier along without anything abnormal turning up in oil analyses. A high-volume oil pump is a good band-aid for that. You'll also hear (on this forum anyway) about piston skirt fractures. I believe the guys here when they say they had the problem, and I've seen a few mentions on the Jeep forums I frequent... but its just not particularly common. The 4.0 doesn't like to run for long above 4000 RPM... so just don't ask it to. Its got enough torque below there, and is losing torque rapidly above 3500 anyway. That'll protect the piston skirts just fine.
Now the 42RE transmission: Not one of Chrysler's finest, unfortunately, but the AW4 used in the Cherokee just wasn't beefy enough for the heavier Grand Cherokee. Things got a whole heckuva lot better when it was replaced with the 545RFE. That said, it can be a good enough unit if not abused. DO NOT succumb to the temptation to use anything except an approved ATF+4 fluid. The 42xE transmissions were second only to the 41TE series in how picky they are about ATF+4. It all has to do with the torque convertor clutch lockup schedule- it really, really counts on having the particular friction modifier package that is in ATF+4 (and +3 before it, but +3 was a vastly inferior fluid). ATF+4 is a solid synthetic fluid by any measure, so you really don't gain much (just a little better oxidation resistance and viscosity retention) by going to Dexron VI, Amsoil, Redline, whatver. Just stick to ATF+4. I wouldn't get carried away with excessive flushing, either. Do a fluid/filter change now, and then a fluid exchange again in maybe a short 20,000 mile interval. While you have the pan off this time to do the filter, think about installing a drain plug through the pan (if it doesn't have one) to make it easy to do a fluid change next time.
