Bimetal

Bimetal:
A bimetal (bi means 2 or double) consists of 2 metal strips that are very firmly bonded together. These 2 strips have different coefficients of expansion. When warmed/heated, these strips bend relative to each other. How much the metals bend depends on the temperature. The warmer the metal gets, the more it bends.
A construction can be made in which the bimetal breaks the contact when it bends due to (excessive) heating. A bimetal is therefore often used as a temperature switch or as a protective safety switch.

Encapsulated bimetal strips are used in cars, among other things, in pistons, the automatic choke, certain dashboard instruments and thermal switches (e.g. the thermal switch mounted on the radiator, which controls the electric fan at a higher coolant temperature) and in the viscous coupling of the engine cooling fan.