How Do Radiator Thermostats Work?

Written by david mcguffin
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How Do Radiator Thermostats Work?
Thermostats help to regulate the engine temperature of a car. (car engine image by itsallgood from

Thermostats are responsible for helping to regulate the engine cooling and heating processes of the radiator system. Although it is possible to drive a car without a thermostat, it is recommended to have a fully functional thermostat in order to maximise the efficiency of your cooling system, maintain emissions safety and save on fuel consumption.

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How It Works

As the vehicle is warming up, the thermostat is closed, preventing coolant from circulating throughout the radiator. Once the engine is at the normal operating temperature, the thermostat opens, allowing hot coolant to pass through the radiator, which is cooled by the air.

Test a Thermostat

Although there are ways to speculate whether a thermostat is working without removing it, there is one way to be sure. Remove the thermostat and put it in a container of water. As the water is heated you should be able to observe the thermostat open as the water warms.

Signs of a Failing Thermostat

Before doing the thermostat removal test, there are a few signs that indicate your thermostat is failing. If the engine takes a long time to warm up to normal operating temperatures, then your thermostat valve might not be closing properly. If the thermostat is stuck in the closed position and is not opening properly, then the upper radiator hose will be cool to the touch while the rest of the engine is hot.

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