So I have a 98 f150 with the 4.6L V8. Been having some issues with it, first off it gets the standard film on the windows associated with a bad heater core, it doesn't leak fluid into the truck tho. But it does have an issue with heat. Also while driving the coolant system develops an air bubble and pushes fluid out the over flow. Also it periodically registers that it's over heating and goes into limp mode. if you press in the clutch and turn the truck off it resets and acts as if nothing ever happened. Please point me in the right direction

 

first thing to do is check for exhaust gas in the radiator coolant system. There are meters to do that.. Next, how often has the antifreeze been changed ? Radiator flushed? Heater core flushed ? Thermostat changed ?............. Some of the older 4.6 with OLD antifreeze have been noted to eat the water pump impeller... If you have not changed the antifreeze in some time, or keep adding tap water, the radiator and heater could be partly plugged..

 

If fluid is being pushed out the overflow it's either boiling out from overheating or you have a head gasket that no longer gaskets. I know O'REILLY Auto Parts rents an exhaust gas tester and I would imagine other parts stores do too. That's where you need to start. Next I would think overheating. If you have poor flow, perhaps due to a blockage, it will cause a hot spot that will give you similar symptoms. While you're at it, a new cap couldn't hurt.