98 F150 - Temperature Gauge and Heat

[jhharris22]

I have a 98 f150(4.6 V8) that has 'seemingly' overheated for about 5 seconds twice in the last month. I noticed the temperature gauge went all the way up after about 1 mile of travel, then it immediately fell back down to normal. The truck has 198k miles.

I flushed out the system using a Peak Flushing Tee, replaced the thermostat with spring facing the engine block, and refilled the system.

I haven't had another overheating instance but I am having problems with my heater....the truck seems to warm up fine and the heat starts off working well. The temperature gauge reads normal for a few minutes then drops and I lose the heat. The truck blows cool air for a while, then will start blocking hot air again.

I believe the water pump has been replaced fairly recently...the pulley has no slack and I don't see any leaks or wetness around the pump or its weep-hole.

I read it could be a blend door or blend door actuator. I don't hear any funny clicking and obviously get some heat.

should I try another new thermostat?

Intermittent water pump problems?

Any thoughts?

[DeltaP]

Make sure the cooling system has been completely purged of all air. Put the heater on full heat when running the eng up to temp and purging out all trapped air. An air pocket can cause the symptoms you describe.