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Role Of A Thermostat In An Automobile Cooling System

Author: Wayne Simms
by Wayne Simms
Posted: Jun 27, 2017

If you take a quick snap shot of the cooling system in automobile you will find that it consists of a water pump which pumps the coolant in the circulatory system, thermostat which regulates the temperature of the coolant, a radiator which extracts heat from the coolant, and of course some plumbing for circulating coolant in the cooling system. The role of thermostat in the cooling system is equally important as others because it regulates the temperature of the coolant.


Thermostat is usually mounted inside housing and located between the water pump and the radiator. When the temperature of the coolant is more, then thermostat senses the temperature and opens up and the coolant flows through the radiator. In a scenario opposite to it when temperature of the coolant is not hot enough then the coolant’s path to the radiator is blocked and it is passed to the bypass system. Bypass system facilitates the movement of the coolant inside the engine and optimum temperature is maintained in the engine block.

The Secret Of Thermostat

The secret of thermostat lies in the sealed copper cup that contains wax and a metal pellet. We all know that the wax expands on heating. When wax expands it pushes the piston and the valve opens up to circulate the coolant to the radiator.

Thermostat also serves the solution to the problem of over-cooling. If the engine is overcooled then it consumes more fuel and the efficiency of the engine lowers. An over-cooled engine wears at a faster rate. A thermostat regulates the entry of the coolant to the engine till the temperature of the engine reaches the operating temperature of the thermostat.

Thermostats are designed in such a manner that they open up at a specific temperature. This is usually termed as the rating of the thermostat. Typically the ratings of the thermostat are 160, 180 and 195 degrees Fahrenheit.

Double Valve Thermostat

It provides greater control on the flow of the coolant as it is fitted with primary and secondary disc valve. The secondary valve is utilized to close the bypass when the coolant starts to flow in the engine. The double valve Thermostat should be used in cars which are exclusively designed for that otherwise the engine of the car may be damaged.

Alcohol Bellows Type

This thermostat makes use of a device called bellows. When bellows get heated the alcohol inside it also gets heated. As a result alcohol evaporates and its volume increases. This exerts a pressure on the bellows. The bellows move as per the mechanical design and open the valve. This is an old fashioned design of thermostat and is often erratic.

Wax Pellet Type

It is the most common type of the thermostats used these days. There is a wax based plastic pellet located on the thermostat valve. As the engine gets hotter the wax starts to expand and the engine side of the valve is opened up. This allows some volume of the coolant to flow to the radiator and some portion towards the engine through the bypass. The volume of flow towards the engine is decided based on the requirement to maintain the normal temperature. was put together by the professionals at US Motor Works (USMW), the manufacturer of electric fuel pumps, fan clutches, automotive water pumps, oil pumps, cooling accessories and other automotive & heavy duty engine parts. Waterpumpu is designed specifically to provide information on automobile coolant systems including water pump installation and system diagnosis, automotive cooling system maintenance, water pump repair or replacement, engine over heating issues, trouble shooting coolant leaks etc. For further details, please visit

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Author: Wayne Simms

Wayne Simms

Member since: Mar 13, 2017
Published articles: 16

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