Transportation Science

Why do cars need thermostats?
Answered by Discovery Channel
  • Discovery Channel

    Discovery Channel

  1. The car thermostat is between the engine and the radiator. It is a small device that holds back the flow of engine coolant until the engine reaches its working temperature. When the engine gets to about 200 degrees F (95 degrees C), the thermostat valve opens and allows coolant in. The reason cars need the thermostat is that if coolant reaches the engine while it is still too cold, it has to work that much longer and harder to warm up, increasing emissions. The key to the thermostat's operation is a small cylinder filled with wax on the engine side of the device. A rod connected to the thermostat valve presses into the wax. When the temperature reaches about 180 degrees F (82 degrees C), the wax melts and expands, pushing the rod out of the cylinder and opening the thermostat valve.

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