Changed thermostat'coolent new an full still heat cold air.blocked grill stl cld

What is your question?

Temps dropped to single digits,changed thermostat,blower working coolint new and full-still blowing cold barely Luke warm air? Can't figure out what's wrong.heater core not leaking that I can see ..I'm stumped??I live in Alaska so common to block airflow with cardboard or bra still not helping.even unplugged fan car almost overheated but still blowing cold air