Thermostat is a key component in the engine cooling system, and its working principle is as follows:

1. Cold start stage: When the engine is started, the thermostat is closed. At this time, the coolant flows through the circuit that bypasses the engine to speed up the temperature rise of the engine. This can reduce friction and wear during cold start and improve combustion efficiency.

2. Reach the working temperature: Once the engine reaches the preset working temperature, the thermostat will open. This is achieved by a temperature sensitive element (such as an expansion valve or a wax-like element) inside the thermostat. When the coolant temperature rises, the temperature sensitive element will expand, which will open the thermostat.

3. Coolant circulation: Once the thermostat is opened, coolant can flow through the engine cooling system, thus keeping the engine in the ideal working temperature range. The coolant dissipates heat through the cooler, absorbs the heat generated by the engine and takes it away. This can keep the temperature of the engine stable and provide the best combustion efficiency and performance.

4. Temperature adjustment: When the temperature of the coolant drops, the temperature-sensitive element will shrink, and the thermostat will be closed. This can reduce the coolant flow to keep the engine temperature stable. If the engine temperature rises again, the thermostat will be reopened to continue the coolant circulation.

The working principle of thermostat is based on the expansion and contraction of temperature sensitive elements to control the flow of coolant. By adjusting the flow and temperature of the coolant, the thermostat can ensure that the engine runs in a suitable working temperature range, improve the combustion efficiency and engine performance, and reduce wear and fuel consumption.

In a word, the thermostat ensures the engine to run in a suitable working temperature range by controlling the flow and temperature of coolant. Its working principle is based on the expansion and contraction of temperature sensitive elements to realize the adjustment and circulation of cooling liquid. This can improve engine performance, combustion efficiency and cooling system efficiency.