A block heater will not help in this situation. And Defrost should work even when idling. If the thermostat is stuck open, beleive it or not, the car can still over heat. The coolant doesn't have enough time to stop in the radiator and cool, so in essence, the thermostat could be stuck open. Or the thermostat could be opening too early
It's normal for the coolant level to go up, it expands since it's warmer. What it comes down to is your heater core not getting a good flow of coolant. There's the coolant level (already covered), the water pump and then the thermostat. One other thing might be a blockage in the heater core but that's somewhat doubtful.
1) At 0.25 gallons per hour, you must save 4 hours of idling to save one gallon of gas. At 20 seconds per stop, that would require 720 stops to save a gallon of gas. PS: Don't believe the ecozealot websites that claim your car burns a gallon per hour idling. Only tractor-trailer rigs do that. See more. Reply Quote.
ri8p.