I have a 97 F150 4x4, 4.6l V8. It only overheats on a cold start. The temp gage goes to hot and the fail safe light comes on but after about a minute the gage goes back to normal and the light goes out. My cap does pop and I lose a little coolant from the res. bottle. I have changed the t-stat, water pump, radiator hoses, pressure cap, temp sending unit, cyclinder head temp sensor, and have flushed the radiator. Also I have noticed that my heater will blow cool air until the temp gage goes to hot and starts to return to normal then my heater will start blowing warm air. Could my problem possibly be my heater core or heater hoses.

 

i had a similar problem. found the thermostat was sticking. also i found out if i filled the antirfeeze tank to the full mark of an inch overfull, that expansion would make the tank go over pressure and cap leak. i now try to keep the level slightly under the cold full mark. have had much less problems. NO problems for first 3 years, no for some reason i have the high temp for 30 seconds then drops back to normal. New thermostat and slightly lower level has helped quite a bit.

 

Take the hoses off going into the heater core and try to flush it out. If it won't flush you will have to replace it.

 

I'd say if you are lucky there is an air bubble in the heater core, either I'd look at it first.

 

I would re-replace the thermostat,and NOT one from Autozone,or the like. Go to NAPA or some reputable parts house.l

 

Removed the heater core hoses and flushed them with water, also did the core. No apparent blockage.