How an Engine Thermostat Works

Inside your car's engine, thousands of controlled explosions called combustion events caused by igniting fuel/air mixture inside the engine generate heat. If this heat is not controlled the engine will over heat and internal damage will occur. These high temperatures are controlled with the help of the cooling system. A cooling system consists of a water pump, thermostat, radiator hose, hose clamps, radiator, radiator cap and coolant. The thermostat is designed stop the flow of coolant through the cooling system while the engine is warming up to operating temperature. An engine needs to operate at a particular heat range to be efficient. Once the engine is warm the thermostat will open to allow coolant flow and cool the engine. Most thermostats are designed to open at about 195° F but other temperatures are available for a variety of applications. A thermostat consists of a main housing, a plunger style of valve and a temperature sensitive wax filled plunger that acts as the sensing and activating device with a return spring. A thermostat maintains engine temperature as is opens and closes

Engine Thermostat

When a thermostat malfunctions it can stick close not allowing the coolant to circulate causing the engine to overheat. Or the thermostat could stick open causing the engine to run too cold. In this case the service or check engine soon light could illuminate, followed by a trouble code. To test a thermostat remove unit. Prepare a pan of water deep enough to cover the thermostat completely. Next install a temperature gauge into the water along with the thermostat. A cooking thermometer works well for this. Next, start heating the water while watching gauge, the thermostat should remain closed until the water reaches 190° at this point the thermostat should start opening and be completely open at about 195°. If the thermostat stays closed through the boiling point the thermostat has failed and needs replacing. If the thermostat is stuck open or broken it has failed and needs replacing. Never run an engine without a thermostat because the thermostat works as a system flow regulator as well. What this means is the thermostat has a specific opening that regulates the flow through the cooling system. If the coolant is allowed to flow to quickly through the radiator the coolant will not have time to transfer the heat it has absorbed. This will cause the engine to overheat.

Engine coolant is used to transfer heat from the engine to the radiator by the cooling system. The radiator removes heat from the coolant by forcing air through the radiator fins. Without coolant your engine will over heat and if left unattended sever engine damage will occur. Coolant colors can vary from green, orange, blue and yellow each having their own protective properties. (Note: coolant and antifreeze refer to the same product, in below freezing, coolant lowers the freeze point hence the name anti-freeze and in warm weather coolant helps raise the boiling point, "coolant")