Welcome to our new beta design! Click here to go back to the old Newschoolers.
my xj blew its head gasket (they 4.0 is pretty notorious for doign that so dont feel like it was your fault) and had it repaired for just over $800 from a mechanic that my old man has used for almost 30 years so he doesnt charge anything over on parts and his labor is a little cheaper
if you dont have a mechanic like that you should look at about 1000-1100..if you go to a dealer you could easily be charged 1500+
no overheating issues + no antifreeze leak = not the thermostat
it's a bad headgasket..and just liek barefootin said just check the oil on your dipstick and that will confirm it
Also, the thermostat has no bearing on whether or not a rear main seal with leak
sounds like you got ripped off by a mechanic