If the motor recieved oil changes and air filter changes religiously, that motor is fine. Do a compression check both cold and hot and see what numbers you come up with. What does the oil look like now? what does the outside of the engine look like?
(dirty or somewhat clean like the PO attempted his best to keep it clean)
My Dad's 96ZJ with 230K+ on the motor still runs great, gets an average of 25 on the highway(bone stock, no mods, lift, larger tires etc). But he took VERY well care of the motor.
My YJ with about 120K+ turns out enough torque and power to break things. But like my Dad, I took care of my motor. And I just installed a turbo on mine and my motor loves it!:evil:
I hear that these motors are very strong if well taken care of. Can go upwards of 300K before a re-build. But I must stress the point, It all depends on HOW the motor was treated!
Some people will say that thier 4.0 died at less then 70K, but I would believe that the motor was abused(lack of oil changes, dirty filter)
My 94 YJ has 167K miles on the I6 and it still runs strong and doesn't burn any oil. The previous owner claimed that he put mostly highway miles on it; that can make a big difference as well. City driving won't run up the odometer like highway driving, but it puts more wear on the drivetrain.
7 main bearings on the crank to help support the rotating mass, no shared journals for rod bearings, and nothing radical on other internal parts make the engine you are looking at one of the greatest workhorse motors that ever came in a jeep. They take mods well other then changing out the oil on time they are realetively low maintence and replacement parts are everywheres. Alot of jeep owners with older jeeps upgrade to the 4.0 motor that came in the 91+ Wranglers.
As long as the motor has been maintained properly, there should not be any issues with it. When doing a compression test, do it both dry and wet. Normally what I would do is check compression cold in all cylinders, then squirt some oil into each cylinder and check it again. Compression should increase about 20-25 PSI. Then start the motor is possible, let it warm up really well and do the same test. Compression between cylinders should be close to the same, within about 5-10 PSI. Also, if possoble, do a leakdown test. This requires compressed air so if you don't have access to a good size compressor you may not be able to do this. Look at the oil filler cap and also the PCV valve. The oil may look clean on the dipstick, but if there's any sludge or build up it will show there.
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