When it gets hot with the air on, turn the truck off and check the radiator for cold spots. If the radiator is not the same temp all the way accross or all over, then you'll need a new radiator. If you have electric fans on the back side of the rad, make sure they are disconnected so as not to hurt your hand.
October, 26, 2010 AT 12:32 PM
I agree with hmac300. Also check between the radiator and a/c condensor in front of the radiator for any build up of leaves or pine needles if the truck has sat under a tree for any length of time. It happened to me. Truck was fine until I turned the a/c on The leaves caused a partial blockage of air cooling the radiator.