Bad radiator, water pump, thermostat, or fan clutch (pretty sure only manuals come with a fan clutch.) Just replaced all of these parts... All very simple... Hardest most tedious part is removing the fan clutch, it can be a serious pain in the ass. Rent a fan clutch tool, no sense in buying one is not like your removing your fan clutch on a daily basis. If you want my advise, replace all these parts at the same time. You will buy part after part, then finally that last part you finally buy was the problem to begin with. Funny because I had a feeling the reason my TJ was over heating, was due to my water pump. Sad part is out of all the parts listed it was the last to go in. Save yourself the headache get all the parts you need then install them together. You'll be glad you did. P.S. Buy a new belt also.