Re: Can someone tell me why
Probably had an air bubble in the system. That part of the cooling system uses the engine Circualtion pump as the means to circulate the coolant. If there is an air bubble in the system, it will stop or seriously slow down the water movement.
Having a cabin heater above the level of the heat exchanger can also cause a problem. Bleed fittings in some installations are necessary since the pumps are not positive pressure pumps like a raw water pump with the rubber impeller.
