How a Car Cooling System Thermostat Works

Inside your cars 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 theengine will overheat and  internal damage can 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  to control 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 to maintain a particular  temperature. 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 with return spring and a temperature sensitive wax filled  plunger that acts as the sensing and activating device. A thermostat maintains engine  temperature as is opens and closes throughout the engine operation.

When a thermostat malfunctions it can stick in the closed position not allowing  the coolant to circulate, causing the engine to overheat. This will cause the vehicle to overheat in a very short amount of time (about 5 minutes). 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 atrouble 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 the thermometer, 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 too 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 overheat and if left unattended  severe 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")

When a thermostat fails it will either stop the coolant flow at operating temperature  "stick closed" or fail to stop the coolant flow causing the engine to run cold longer  than necessary. If the thermostat fails "open" it will cause the coolant to continuously  flow through the engine causing a diagnostic trouble code (check engine light) to  be set by the computer. When a thermostat sticks closed it will cause the engine  to overheat quickly, usually within 5 to 15 minutes of operation. To check for either  of these conditions, drain coolant and remove the thermostat (under the thermostat  housing) if you are unsure of the location of the thermostat on your engine consult  a car repair manual.

Once you have removed the thermostat inspect the condition of the main body check  for any cracks or broken pieces and check the valve to make sure it is closed. If  the valve is open the thermostat has failed and needs to be replaced. To check the  operation of the thermostat prepare a pot of water on the stove deep enough to cover  the thermostat completely. Place the thermostat in the pot of water, turn the stove  on a medium-high flame, the thermostat should open right before the water comes  to a boil. If the water has boiled and the thermostat valve is still closed the  thermostat has failed and needs to be placed.

Basic Checks

Low levels of coolant can lead to problems related to engine overheating. Always  maintain proper levels of coolant in the overflow coolant reservoir tank. ONLY!  Check the radiator when the engine is cold. Only add antifreeze and reinstall the  cap properly.