scottbit,
The problem 99% of the time is a old, plugged radiator.
A thermostat can stick, but this isn't normal. If you truck does this every time, that means the thermostat would have to malfunction the same way every time too...not likely.
You installed a new thermostat...why! Was the truck doing the same thing with the old one?
The gauge is showing hot...is the engine actually hot. You can smell/feel a hot engine.
A thermometer in the fill spout would confirm the accuracy of the dash gauge.
Did something happen to the truck before this happened. Did you tune it up and time the engine.
The plugged cooling system system would not allow the engine to cool down and run normally after sitting a spell, it would always cause the system to run hot.
I think the course of action would be to see if this actually a periodic heating, or is it really a constant problem while running the engine.
The thermostat has to be installed with the proper side to the block. If you want, you can remove the thermostat and see if this changes the chain of events.
Stuart
