Should I Change the Thermostat?

CARS.COM — A car thermostat is responsible for preventing your engine from overheating. Unless an engine overheats or fails to reach normal operating temperature after being driven for several miles, the thermostat that regulates the flow of coolant is probably working properly. Thermostats generally last for years — even for the lifetime of a vehicle — so why bother changing it? Does a car thermostat need to be changed as part of normal maintenance? Let's take a closer look.

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What Does a Thermostat Do? 

Your car's thermostat is a vital component that is actually pretty simple. It's a valve located in your car's cooling system. Its job is to regulate the amount of coolant that is recirculated back into the engine and how much is cooled via the radiator prior to being recirculated. This ensures that the coolant in your engine stays within a specific temperature range regardless of the outside temperature. The valve is opened and closed with a spring, piston or another thermally controlled device. 

When to Replace Your Thermostat

Because they are so simple, thermostats generally do not go bad with age. Indeed, if it appears to be working, there probably isn't a need for a new thermostat. However, if you're having other cooling system maintenance performed, such as replacing the coolant and/or radiator hoses on a vehicle that's been in service for several years, it could be a good idea to replace the thermostat at the same time for peace of mind. That's particularly true if the upper hose is being removed, as that's where many thermostats are located. If you need to have your radiator or any gaskets or hoses replaced in your cooling system, you may also want to ask your mechanic about whether you should replace your thermostat at the same time. 

Aside from this type of preventive maintenance, a thermostat doesn't need to be replaced unless it stops opening and closing when it's supposed to. If it sticks in the closed position, that traps coolant in the engine so that it overheats. If it sticks in the open position, the coolant will constantly circulate through the engine and radiator, which can prevent the engine from reaching full operating temperature (and full efficiency) and reduce heat output from the climate system.

Among the signs that a thermostat isn't working are an engine that overheats or runs hotter than usual, or a cabin heater that fails to produce sufficient warm air. A faulty thermostat may also trigger the check engine light. Because these symptoms can be caused by other problems, the entire cooling system — from main components to small gaskets — should be inspected by a pro before deciding to replace the thermostat.

If your vehicle has ever overheated, you will likely need to get a new thermostat. Overheating can cause serious damage to the valve as well as the thermostat housing and the hoses and gaskets that are a part of your car's cooling system. Excessive heat can cause things like hoses, gaskets and even metal thermostat housings to warp and lose their original shape. When this happens, these vital components are no longer able to do their job as they should. 

Don't Ignore a Damaged Thermostat

Not getting enough heat in the interior is mainly a comfort issue, but overheating can cause serious engine damage and shouldn't be ignored. Most vehicles have a temperature gauge that gives a constant reading of the cooling system temperature, ranging from "C" to "H" or blue to red. In modern cars, the needle or bar graph will come to rest dead center, or just a notch or so toward the cold side, when the engine has reached optimum temperature. Cars with this gauge might also have a warning light for when the engine is running hotter than normal.

An increasing number of cars do away with the gauge and have a high-temperature warning light, either alone or supplemented by a separate indicator — typically a blue icon of a thermometer sitting in water — that comes on when you start a cold engine and stays lit until it reaches the proper operating temperature. If this indicator stays illuminated, there's a good chance the thermostat has stuck open.

A gauge can give a driver an early heads-up that something is wrong, but a warning light might not come on until the engine is so hot it needs to be turned off immediately to prevent damage. If your vehicle is overheating or you have any other reason to think your thermostat is going bad, have a professional inspect your entire cooling system, including your radiator, thermostat housing, and all gaskets and hoses.

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