Here is my problem: While driving the heater looses all heat and starts blowing cool air. After a few minutes the temp. gauge goes from normal to pegged high, coolant runs out of the overflow tank. I shut off the heat for a few minutes the gauge goes back to normal and the heat returns.

I seen this problem on a earlier thread and the OP said he was told it was the head gasket, but I'm not so sure it's the head gasket. There is no coolant in the oil, I just changed it today. Also I don't think there is any coolant in the exhaust, exhaust is burning clean, no smoke and no coolant smell. I changed the Thermostat and it didn't help. I really hope it's not the Head Gasket, due to being active duty military I just don't have time to repair it. Any ideas?

Note: I have a 2003 Ford F-150 w/ 83,300 miles.

 

Well it sounds like a head gasket. However the best way to determine if thats the problem is to have a Hydrocarbon test performed or rent a hydrocarbon detection kit from an auto parts store such as Auto Zone, Napa,
etc.
If the test shows hydrocarbons one or both head gaskets are blown.
FYI My 97 4.6 had the same symptoms and I had no white smoke or coolant in the oil. Rightside head gasket however was blown. Have you changed the thermostat and topped off the coolant ?However I personally doubt its a t-stat with those problems. What happens is the combustion chamber is pressurizing the cooling system with combustion gases through a blown seal (head gasket) a large air bubble forms and when that hot air bubble passes over the temp sender the gauge spikes. The air keeps getting pumped into the system, it pressurizes it and the coolant gets forced out of the degas bottle some guys It is about a 15-20 hour repair to replace both head gaskets. Took me around 18 doing it alone. Good luck

 

When the truck is running and up to temp, grab the coolant hose from the top of the intake to where it enters the top of the radiator. If you can feel bubbles through this process then it is almost definitely a bad head gasket.

Also if you find that it is a bad headgasket you should plan on having the heads checked to make sure they aren't warped.

Best of luck.

 

Thank you for the help. I did have the hydrocarbon test done today and found out that indeed it is a blown head gasket. I'm going to get the gasket kit and do the work myself. I'm not sure when I'll get around to it. I picked up a bottle of Blue Devil and I am going to put that in this weekend, hopefully I can prolong this for a month or so until I get the time to repair it. I plan or taking the heads to a machine shop to have them NDI'd for cracks and checked for signs of warping. Since everything is torn down I plan on replacing the plugs, and flushing and replacing all fluids also. Should run good as new when I'm done.