What Does a Car Thermostat Do?

Man holding used car thermostat, What Does a Car Thermostat Do?When you imagine a thermostat, you might think of the box on your wall that allows you to control the temperature inside your house. In a car, you may assume it is the controls in the cabin of the car that performs the same function. However, a car's thermostat is much different. So what exactly does it do? We've done the research to tell you precisely what a car thermostat is and what it does.

A car thermostat's primary function is to heat the engine to its desired temperature when you first turn it on and then keep it at the same temperature for the duration that it is on. The thermostat works closely with the coolant to either allow or block it from cooling down the engine.

Keep reading below as we answer related questions and talk more about car thermostats.

How Long Does A Car Thermostat Last?

Luckily, car thermostats are not known for going out or malfunctioning very often. Most thermostats will last well-0ver the life of your vehicle. Car thermostats themselves may be working fine up until they require replacement over a reason that has nothing to do with them breaking.

It is estimated that a car thermostat could last well over ten years or more before going out. But again, they could last much longer than this if correctly cared for.

How Do Car Thermostats Work?

Car thermostats last so long because they are a simple piece of machinery that performs a simple task. All it has to do is either open up to allow coolant to flow through or stay closed, so the engine warms up. Having this be the only function of the car thermostat extends its life dramatically because there are not very many moving parts.

What Causes A Car Thermostat To Go Bad?

Close up detailed shot of a car thermostat with white backgroundThere are many reasons a thermostat may go bad. One of the most common reasons is the engine gets too hot. While a thermostat is made to solve this problem, if an engine gets too hot and goes beyond the range the thermostat is made to handle, it can cause damage to the car thermostat resulting in failure.

The thermostat can also break due to a thick paste-like substance that the coolant can turn into over time if exposed. If the bad coolant tries to flow through the thermostat, it can get clogged and cause it to malfunction or break.

Other ways a thermostat can go bad are more common than the ones already mentioned. Age could cause one to break, as age can affect everything. The thermostat also could not have been made or installed correctly. This would possibly allow for it to perform smoothly for a certain amount of time before finally giving up.

What Are The Symptoms Of A Bad Thermostat?

If you experience any of the following symptoms or you notice the temperature warning light appear on your gauge cluster, then your car may be at risk of overheating, or any of the other problems that go along with a bad thermostat.

For one, most vehicles have a temperature gauge in the cabin of the car. It looks similar to all the other gages except the needle will typically stay in the middle after the car has had a chance to warm up. If you notice your vehicle's temperature gauge rising higher than that, it could be a sign of a bad thermostat.

Another symptom similar to the one above is if your temperature gauge is moving sporadically. When a vehicle first starts up, it is normal for the needle to rise slowly to around the midpoint. This sometimes can take as long as ten minutes, depending on how cold it is outside. If it rises quickly or drops quickly, then something may be wrong with the thermostat.

Finally, if you notice any sort of coolant leak then there may be something wrong with your thermostat. Since this is the only liquid that comes into contact with the thermostat, it could mean that the thermostat is stuck in the closed position and forcing the coolant to leak.

Close up shot of a car thermostat

Can You Drive With A Bad Thermostat?

It may run, but you should not drive it. While you can technically drive with a bad thermostat, your car is eventually going to either shut down or overheat. When a car overheats, almost anything can happen, including a fire. For this reason, we never recommend driving a car if you notice the thermostat could be malfunctioning.

Not only could it be hazardous, but it may worsen your problem and cause even more damage. By driving your vehicle with a broken thermostat, you risk the irregular temperatures ruining many other parts of the car.

This could result in serious injuries or even death. Your best bet is to have someone look at your vehicle or have a tow truck take it to a mechanic.

How Much Does It Cost To Replace A Car Thermostat?

Even though a broken car thermostat can cause a lot of damage, it is relatively inexpensive compared to other significant repairs. A car thermostat can cost anywhere from $125 to $200 to replace depending on where you take it. The part is relatively cheap, running around fifty dollars. However, you will end up paying approximately one hundred dollars or more for labor because it requires time and effort to locate and replace the thermostat.


Overall, a car thermostat is a small piece of a large engine, but it is one of the most essential parts of a vehicle because it keeps everything at the correct temperature. Without this "gate-keeper" functioning properly, it may keep out coolant and cause the engine to burn up, or let too much in and cause it to freeze over.

If you notice any of the symptoms associated with a bad thermostat, make plans to take it to a professional immediately so they can diagnose your problem and repair it correctly the first time.

For more information on situations related to car overheating, check out these posts on Vehq.com.

Driving With Low Engine Coolant -- Is It Safe?

Car Overheats When Idling -- What Could Be The Matter? [And How To Fix It]

What Causes A Car To Run Hot While Driving?

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