step son has one,looks like head gasket time,any real problems that stand out about this?,are they prone to crack/warp?,it has 140000 on it,will run 50 miles or more and just push out some water,system stays pressured up for a couple days if you dont loosen the cap,it looks to be all aluminum with cast iron sleeves,do the blocks warp on these also?,any feedback on this would be helpful
thanks in advance!
Butch

goin with a used engine!

You have a lot more miles on yours than my wife's Nitro. I have been inside the timing cover due to a water pump leak. I have not heard any terrible stories about the 4.0, at least not like all the ones about the Durango/Dakota 4.7L. The key to longevity with these engines is making sure that they never ever overheat. My Durango warped a head at 220,000. Luckily, I got to the 4.0 before any damage was done. Before installing the used engine, replace the water pump and timing belt as getting them in and out with the engine installed is a pain. Doable, but a pain.