Rep Power: 0

I have a 2004 EX coupe. Once the car is warmed up and if i turn the heat on sitting still it will start to over heat and blow cold air. Now if I am driving 55+ it will blow hot air like a champ until I slow down and then it will start to overheat again. anyone had this happen or know what it could possibly be? I have thought about doing the small things like the thermostat and a flush, but could it be a bad water pump? I have a little over 81k on the clock.

 
Rep Power: 0

Bad water pump or head-gasket is leaking air into the cooling system and you have low coolant level. Look at the reservoir and see if it's near full or overflowing. I think if the thermostat was stuck closed (or hard to open) you would still get hot air from the heater. I bet it's the pump. Might be worth checking thermostat and coolant level, possibly new radiator cap. Those are the cheap things to check for.