I have a 1999 Ford F-150 with 199k miles and in July had to replace the water pump (brand new O.E.M.), As the breather hole was seaping water. Had it replaced. Everything was good. About a week ago, it got cold and turned on the heater and it didn't get to warm. Day before yesterday, the engine temp started running hot (never reached overheat, because I turned on heater with blower on high). No heat came out of the vents, but the engine cooled down to normal. I suspected the thermostat, as it had never been changed to my knowledge. It still overheats and the heater just gets a little warm. I suspect that it may be the water pump causing the problem. I did check the radiator and flushed the system out, while I had the cooling system open. I, also, pulled the heater hoses and flushed out the heater core. I do my own mechanic work with the proper tools. I am baffled as to why it is overheating. One thing that I noticed when it started overheating, is that when I released the pressure cap, the tempature did immedeatly go back to normal, which shows the sign of a blown head gasket from the water jacket to a cylinder, but no other symptoms (rough idle or white smoke out the tail pipe).
Sunday, November 28th, 2010 AT 2:45 PM