Heating and cooling problems
 

I own a 1997 f150 4.6l with 358,plus miles on the original engine and have owned this from brand new.
The problem I'm having is with cooling system. This problem started about a month ago or so and everything I've done has not fixed the problem. The problem is that the when I start the truck in the mornings when the engine is cold and drive to work, which most mornings only takes me 5-10 minutes the temp gauge will start to show a temp rise and some heat coming from the heater, the temp gauge will drop to cold and no heat from heater and over pressurize the system and force coolant out of the reservoir. So I replaced thermostat and got the same problem, replaced with another thermostat thinking got a bad one, same results, so replaced tstat with lower temp one and guess what, same thing. Thinking maybe I got air in system I let truck run for half hour or so. The next morning same thing.
I have since replaced the water pump, maybe it was corroded and not moving coolant, not the problem. I just replaced the radiator with new one, same results. Heater core was replaced 2 years ago and is doing fine.
I'm frustrated to no end and could use suggestions.

You have a leaking head gasket(s). With that many miles its time for a new engine, or a replacement vehicle.