The thermostat controls the engine coolant temperature.
When the coolant temperature is below the operating range, engine coolant is bypassed back to the inlet of the
water pump. When the engine coolant temperature reaches the operating range, the thermostat opens, sealing off the bypass, forcing engine coolant to flow to the radiator or the heat exchanger.
An incorrect or malfunctioning thermostat can cause the engine to run too hot or too cold.
Never operate the engine without a thermostat.
Without a thermostat, the path of least resistance for the coolant is through the bypass to the water pump
inlet. This can cause the engine to overheat.
The thermostat contains two check balls to vent air past the thermostat when it is closed. This helps to vent air
during the cooling system fill process.
