A car thermostat does not have a recommended service interval. If proper cooling system maintenance occurs, most thermostats will last for years, if not the vehicle's lifetime. It is recommended only to change your thermostat when and if it malfunctions. Most car owners choose to replace the thermostat during routine cooling service, as it's pretty cheap to replace a car thermostat anyway. Taking this preventative measure will ensure that corrosion does not reach your cooling system's components.