!997 ford f-150 heating

[x1957x]

Does it have an area where it sucks cold air into the heater core holding area? Reason is that when I sit and idle it blows HOT air on low but when I drive down the highway it starts to cool down drasticly. Any idea's are appreciated.. Is there a vaccum hose or the controller that can do this or is it the heater core?

[Jeremy airjer W]

I think you have a bad thermostat.

Is there heat if you have the blower set to higher settings?

What does your temp gauge do when you drive down the road?

[Scott K]

It may also be low on antifreeze.

[Jeremy airjer W]

It may also be low on antifreeze.

Wouldn't the opposite be true? No heat at idle plenty of heat driving?

[Scott K]

I have seen the water pump cavitate, and cause foam in the cooling system under higher rpm, but at lower rpm, the coolant would settle lower, and cover the fins on the water pump, but in most cases, you are correct.

[Jeremy airjer W]

Interesting! I can honestly say I have not run into that.