Sixer4Life

For about a month now my mustang will randomly blow stone cold air out of the heat. It will only do it if I've been driving it a few minutes then it sits and idles while warming up. But once I push it above 2500 RPM or above 40 mph it will go back to blowing out burning hot air.

Coolant was just put in and tests at -45. I was thinking maybe the thermostat was getting stuck but not sure. Anyone else have any ideas?

Daehawk

Usually happens with low coolant so since that is good and works if pushed I agree with your therm deduction.