Need a little help... I have a 2004 F150 Lariat Screw. I'm getting sporadic heat. Sometimes heater works just fine.... Others, I get nada... (Was on the hwy for over an hour, never got warm) (Another "trip" went to store, 5 min away and it was HOT)

I've read a couple of post about heater cores and blend doors... I know what a heater core is/does, but have no idea on the blend door.... I guess my problem could possibly be a sticking thermostat as well.
I don't have any leaks. Nor do I smell antifreeze.

Any ideas? How to fix? cost?

 

Couple of questions: Does the air blow out at your feet ( either hot or cold )? can you get heat to blow out the console/dash?

 

The air will blow where ever I tell it too.... Feet, dash, defrost.... everywhere....

 

feel your hoses at the firewall going to the core. if they are hot maybye core is partially plugged up. a good flushing will take care of that. had same symptoms on my dakota,after a flush it was like a blast furnace lol.

 

Other options?? Possible causes/solutions?

Thanks