Any liquid-cooled car engine has a small device called the thermostat that sits between the engine and the radiator. The thermostat in most cars is about 2 inches (5 cm) in diameter. Its job is to block the flow of coolant to the radiator until the engine has warmed up. However these little gadgets tend to fail and with that a whole lot of problems occur which will lead to very costly repairs or engine changes. It's advisable to change the thermostat when it fails. This Item is new and fits various Mazda engines.