Heat problem in my F150?

Question

I have a 97 f150, with a 4.6L motor. When I turn the heat on. It will blow hot for about 30 seconds, then cool off. If I shut it off for a minute or two the same thing will happen. I have changed the thermostste, and checked all the fluids.

What could be the problem be?

Thanks Driver58

Answer 1

your heater core

Answer 2

heater core block

get a good can of  rad flush  drain rad and engine block

there drain plug for coolant on engine

if prob still there change heater core

but if u lose coolant not same repair

Answer 3

take the heater hoses off and flush out the heater core, it,s probably half clogged up.