How an Engine Thermostat Works

Published: 14th May 2010
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A thermostat is one of the indispensable components of your car engine. Its malfunction can lead to disastrous consequences.

Ever wondered what happens inside the engine of your car? Inside the engine of your car, fuel reacts with air to give rise to multitudes of controlled explosions. These are called combustion events. These combustion events inside the engine generate heat. This heat needs to be controlled. Why? If this heat is not controlled the engine will overheat and internal damage can occur.

These high temperatures are controlled with the help of the cooling system. This heat is transferred from the engine to the radiator by the cooling system using an engine coolant. The radiator forces air through the radiator fins to remove heat from the coolant. Without coolant your car engine will overheat and if left unattended severe engine damage will occur.

A cooling system comprises 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 the coolant to flow in order to maintain a particular temperature. A thermostat maintains engine temperature as it opens and closes throughout the engine operation.

Most thermostats are designed to open at about 195° F. 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.

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. This results in overheating of the vehicle in a very short amount of time, usually within 5 to 15 minutes of operation. Any of these conditions can be checked by draining coolant and removing the thermostat placed under the thermostat housing. Once the thermostat is removed, the condition of the main body is inspected; it is checked for any cracks or broken pieces and also the valve is checked to make sure it is closed. If the valve is open the thermostat has failed and needs to be replaced.

Never forget to check the thermostat! You can prevent your engine from overheating by checking the efficacy of your thermostat. This is possible by immersing the thermostat entirely in a pan of water. A temperature gauge is also interested. The water is heated. The thermostat is expected to 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.



This article is one of those many which focuses on an engine part of a car. The content aims at deepening one's knowledge and instilling interest in engine parts.

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