How Does a Car Thermostat Work?


Keeping It Warm and Cool

  • A car thermostat does just that, it keeps the vehicle warm but at the same time cools the engine block. All engines, more importantly car and truck engines, must maintain a certain temperature for proper operation. If the engine is too cool then mileage will be affected by using an improper fuel mixture. If the engine gets too hot, it can be severely damaged from parts malfunctioning, or metal parts may warp from the excessive heat.

Temperature Ratings

  • All thermostats for cars are rated by temperature. Engines come in all different sizes from small economy models to ones that can pull a large load. They all have the same thing in common: they must be temperature controlled. Thermostats are rated in degrees so they can be controlled for proper cooling. Before the advent of computer controls placed in cars, some automobiles would have to have their thermostats changed out depending on the season. In summer it may have to be lowered to 165 degrees F. While in the winter it may be raised to as high as 195 degrees F. The purpose was for proper engine operation and engine power.

It's All in the Spring Disc

  • Basic thermostats for cars are all constructed the same way. They may use different materials, but the action still creates the same result. Two metals of different types are sandwiched together. When heated these two metals move against each other causing them to open or close. These discs are held in place by a spring of a certain tension. All thermostats are normally a closed valve. When the temperature reaches a certain point these discs move against the holding spring and open the cooling circuit. The coolant is then allowed to flow through the engine into your car heater and then through the radiator to be cooled. The car's water pump creates the flow for the plumbing circuit.

Computers Change the Thermostat

  • In today's cars, the parts may have changed but the action and principle remain the same. Instead of the spring disc thermostat, solenoid valves are now employed in certain cars. These solenoid valves use the vehicle's 12-volt direct current electrical system to open and close the coolant circuit. The flow path is the same but it is much more sophisticated. A sensor is placed in the coolant line that accurately reads the temperature. This sends a signal to the car's computer, which in turn will open or close the electrical thermostat valve. A separate fan is now employed on the radiator to keep the coolant at a very precise reading. The result has created a vehicle that can be accurately controlled for performance and fuel mileage. Regardless of the technology employed, all thermostats still perform the same function, to keep the car's engine at a certain temperature for optimum operation.

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