What Chris said.
Also I know the XJ 4.0 is notorious for catching air in the cooling system. I think a fix is to park with the front higher than the rear and add coolant as air burps out of the radiator cap.
The under carriage has been undercoated, the dealer undercoats all his vehicles. There are not signs of rust anywhere that I could see. It's a Texas truck SOUTH Texas that is. No road salt here just what we get from the Gulf breezes.