I have a 88 k1500 Silverado with 5.7. When temps get cold out especially in the below zero and.colder range, my heater is blowing cold. My stat is working as it reaches about 200-210 then opens and drops to 190 or so. Both heater hoses are hot and air is nice and warm above 20 deg or so outside. The temp control is moving the blend door and have good blower flow. When temps get really cold the engine temps go down to 150 and sometimes even less. I am thinking a cold weather front would be best start to keep airflow from radiator and get engine temps up. Any suggestions ?