Why do some people here resort to calling people idiots???
I have owned 3 Jeeps with 4.0L's. To be quite honest I'm not very impressed. Yes many many of them see very high mileage, 200K+, but not all of them do.
My '89 had piston slap noise at 70K. It never affected it much other than being annoying. It also developed a severe leak at 120K miles.
My '98 has actually been very good to me. At 133K miles it is still running very well. But although I think the 4.0 has plenty of power for rock crawling, not much power is needed, this motor is way under powered. I have towed with my '98 since it was new and I have always longed for more power. With a 3Klb camper I can barely make it up the mountains in CO. It also has a really hard time in NE, actually it has a hard time anywhere. I would love to do a V8 conversion. On top of that performance parts, or even stock parts, are rediculus for the 4.0.
This brings me to my wife’s ‘01. At 78K the motor crapped out. Apparently from a bad head gasket (water in the oil). A second motor crapped out in 3K. The newest motor seems to be doing fine. But when I was considering doing a stock rebuild on it I was shocked by the price of parts (pistons, rockers, etc). I think strokers for the 4.0 are just insanely priced. I can do a 347 Ford for about the price of a stock 4.0 rebuild. (Yes I know there is more to the cost of putting in a V8 but I'm just saying the 4.0 strokers are way over priced).
If my '98 ever needs a motor I'll likely just get a replacement motor from a recycler but I will be thinking long and hard about a 5.0L V8. The 5.0L has great torque, lots of power, great support, and are very compact. But in all likelihood it would be too much work. But I'll still be thinking about it.
That said I wouldn't go with a Jasper motor or any others. To keep costs down they have to be using really low end parts. I would get a low mileage motor from a yard any day. Mine even came with a lifetime warranty.
HTH,
B-loose
