Longevity of a late 90s 4.0 in a TJ

BigClay

BigClay

Knower of useless ZJ things
Joined
Sep 24, 2008
Location
Winston-Salem
How many miles can a late 90s 4.0 in a TJ go before it will need a rebuild? I had a 93 4.0 once with 160k miles and besides lifter clicking it ran great. So is 200k about max, is 250k max? What normally goes first, and is that a catastrophic failure?
 
I had a xj with a 4.0 in that I bought from the original owner in pristine condition with 290k on it for $900. Sold it with 298k on it for $900. The kid I sold it to still drives it everyday and I talked to him a year ago and its going strong at 340k (and 2 fuel pumps later). However, I hear of some needing rebuilds in the early 100k range. I think it depends on how they are taken care of.
 
Taken care of, Im not sure they ever die! :D

I know of 4.0s that have had lifter noise for 60k+ miles! Only common, if even that common, is head gaskets. And I think these are generally engines that have been percolated several times
 
I'd say 200k is about the magic number. They will undoubtedly last longer, but at that point, everything is pretty old and durability rests heavily on how well it had been cared for up to that point. The 2.5L in our Jeep didn't make shit for oil pressure at 220k, but ran fine until it burned a valve.
 
My 96 xj has 197k and still holds 40psi at idle. No smoke, no leaks, no noise. I bought it with 184k and it seemed to be serviced well. Only time will tell.
 
The 4.0 in my TJ made it 47k miles, then the pistons melted.
The 4.0 in my wife's XJ has made it 240k miles and is still going strong. No funny noises and uses about a quart of oil every 3k miles.
 
I know a stroker is the best bang for the buck but it is also more expensive; so what would be an estimate for a stock rebuild on a 4.0?
 
My dad's TJ is around 212,000 miles, runs great! We replaced the water pump, starter, and spark plugs and it runs like all of the other jeeps around here.
 
got 215,000 on my 2001...yea,it ticks. Engine is doing good with 40psi oil pressure at idle and around 60 at cruising speed.Oil consumption is nill.Small seeps at the rear main and valve cover gaskets. Ran synthetic oil till 200,000 miles and now I run dino.Oil is clean when I change it at 3 to 4 thousand miles. The ticking started at roughly 160,000 miles.
 
Our Cheap Truck Challenge 89 XJ still runs great with about 190k miles and a hole in the side of the block. Our ECORS 98 XJ has 229k miles and it runs great too.
 
My '99 is at 200k and just now started the infamous rear main seal leak. It's never had an oil change last longer than 3,000 miles.

No knocks and the heads look clean for that many miles
 
there is a head casting that is kind of weak around 2000 to 2001 and it can crack.Also high mileadge 4.0s can lose a piston skirt too with number five being the prominate one. Both of these problems aren't coffin nail drivers tho and can be handled with a little initiative and creativity.
 
ord.sgt.26NC said:
Also high mileadge 4.0s can lose a piston skirt too with number five being the prominate one.
Click to expand...
This is what happened to mine with 260k on the clock. Also lost #5 at around 130k. I just replaced the Piston, rod and bearings on that cylinder then. That motor still had the cross-hatching visible with no lip at the top of the cylinder at 130k miles.
 
My old jy had 360k abusive miles on the clock and still ran strong. Used a little oil but ran great. My current xj is at 178k and runs like a new jeep. Its all in keeping them maintained.
 
Our '99 XJ has about 175k on the clock and runs GREAT!! Only major work I've had to do to it was change out a head gasket. I have used Shell Rotella T, and throw in a lil STP oil additive w/ zddp, since I bought it 6 years ago. I run that in all my 4.0's they seem to like it. I don't know if it really helps, an old mechanic friend of mine suggested it years ago and it's never hurt anything.
 
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