Any harm in running the heater on high in this hot weather after a coolant change?

[The motor guy]

Isn't this what your supposed to do when you do a coolant change - to get any air bubbles out?

Also an old trick if your car is overheating - roll down the windows and turn the heater on high

A lot of vehicles circulate coolant regardless, so I'd verify that before you turn the cab into an unnecessary sweat box.

 

[Chris142]

On most modern cars, coolant flows through the heater core at all times, doesn't it?

The blend-air door has replaced the old system with the mechanical valve in the incoming heater hose.

I believe that some cars still use a heater valve. But most just use a door now to determine the outlet temps.