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).
My 2002 Nissan Sentra (150k miles) is acting similarly. No blown Head Gasket, Water Pump and Thermostat are good.
Does not happen everytime, but maybe once or twice a month. When this happens the engine will get Hot (close to the "H") but the temp will go up and down between 2/3 hot and hot (thermostat opening and closing).
What I have noticed when this happens is that my Overflow tank gets completely full. Like your truck, if I crack the Radiator cap, to vent, the cooling begins acting normally and the heater works fine. The last time it happened, I pulled over, vented the radiator, and literally blew into the overflow tank to get the fluid back into my radiator. Hunky-Dorey after that so far.
Several mechanic friends of mine are stumped. I have had my Radiator and Cap pressure tested, and they're fine.
My best guess is there is some kind of "vapor" lock, or maybe reverse vacuum, that keeps the water in the radiator when the Theromstat opens for the first time. From then on the fluid just goes into the over flow.
I am going to try "back filling" my system by removing the thermostat and then the lower hose from the radiator and pouring coolant into the hose until the hose (and hopefully engine) is full. Reconnect the lower radiator hose and thermostat, and then top off the radiator.
Hopefully, with the cooling system truly "filled" I won't have this vacuum or vapor lock issue any more.
Still trying to figure this one out. It's ridiculous to have an over heated engine whole you're freezing you tail off inside the vehicle.
November, 29, 2010 AT 2:47 AM
If you ain't done it yet, I'd snatch out YE OLE thermostat and replace itI stick a new one in both of my Jeeps every SPRING. Need it or not! They will Build heat sometimes, then suddenly open and all seems fine. But you'll be stuck somewhere--someday if you keep it!
"Mr. Jeep" is 33years Young---"Willy" is 64 Years young. Both are Daily Drivers
November, 30, 2010 AT 10:22 AM
I found my problem. It was in fact the radiator cap. Replaced it, even though it tested out fine. No more problem. For the first guy that answered me, sound like the problem that you are having is the lower radiato hose is collapsing. Either replace it, or as an option that works, take a metal coat hanger and wrap it around a shovel handle until it looks like a spring and slide it into the hose. What this will do is keep the hose from collapsing completely, allowing water flow and not ceiser of flow. This will prevent this from occurring. Hope that this helps.