Thermostat is a device for maintaining a static (constant) temperature, as its name implies. There are thermostats of different designs in many devices and mechanisms, from water heaters to refrigerators. There is also a thermostat in a car's internal combustion engine (liquid-cooled, of course). In a car, the thermostat regulates the temperature of the coolant (antifreeze): it accelerates the warm-up of a cold engine and provides heat removal from the hot one. Therefore, the engine works more efficiently and more comfortably for the driver, especially in winter - without a thermostat, the stove would usually blew cold air.

1. A6 (4A2, C4)
2. A6 Saloon (4A2, C4)
3. A6 / S6 (4A2, C4)
4. A6 Avant (4A5, C4)
5. A6 / S6 Avant (4A5, C4)
6. 100 Avant (4A5, C4)
7. A8 (4D2, 4D8)
8. A8 Saloon (4D2, 4D8)
9. A8 / S8 (4D2, 4D8)
10. A4 (8D2, B5)
11. A4 Saloon (8D2, B5)
12. A4 / S4 (8D2, B5)
13. A4 Avant (8D5, B5)
14. PASSAT (3B2)
15. PASSAT Saloon (3B2)
16. PASSAT Variant (3B5)
17. PASSAT Wagon (3B5)
18. PASSAT Estate (3B5)
19. A6 (4B2, C5)
20. A6 Saloon (4B2, C5)
21. See more in applications

The principle of the thermostat work

The classic VALEO brand Thermostat, coolant is a movable valve that moves due to a change in the external environment - heating or cooling of antifreeze. The thermostat is made of a thermoelement filled with a substance resembling wax in structure - ceresin, with the addition of copper powder, graphite or aluminum for better thermal conductivity. At a certain temperature of the antifreeze, ceresin expands, opening the thermostat valve. When the motor cools down, ceresin contracts and the thermostat closes again.