Heater Problem

I have a 2000 SR5 V6 with 270,000 miles that I put on my self. This truck has been driven off road and has done some towing. It has been a great truck!
The problem I have is with the heater. The heater works while driving normal, but when stopped and running the engine at an idle the air turns cool. Any ideas?

Thanks Rob

 

I would start with looking at the thermostat, followed by a drain and flush cycle of the cooling system, perhaps with a bottle of the cooling system cleaner...do it with heater full on and I would run the vehicle around town for a couple of hours with the flush in, before draining, refilling, running to full hot, draining and finally new antifreeze. New hoses, belts, radiator cap, fan clutch, thermostat at this point in time isn't a bad idea either.

Howard