Why does my thermostat stay open when the heater is turned on

Question

Everything works fine until I turn on the blower for heat

Answer 1

The engine coolant thermostat open and close with the coolant temperature, there is nothing else controlling the thermostat. If the coolant is cold the thermostat stays close (no coolant flow) and as the coolant warms up, the thermostat start to open. Faulty thermostat, low coolant or air in the coolant system can cause an improper thermostat operation.