A thermostat is a type of valve that regulates the amount of coolant circulating in the engine and radiator. It also ensures that the coolant stays within a specific temperature range irrespective of the temperature outside the car. 

Usually, it doesn’t need replacement so frequently. But it is advised to change it along with other parts such as the coolant or radiator hoses, etc. Some of the signs suggesting the need for replacement are:

• Overheated engine
• Improperly heated cabin air

The average lifespan of a thermostat is about ten years, but it may become worn out sooner or later based on several factors. So, it is advisable to get it checked from time to time or look for the above signs.