What Does a Car Thermostat Do? Deciphering a Faulty Thermostat!

Do you want to know everything about a car thermostat? What does a car thermostat do - Is the working of a car thermostat intriguing you? When is the right time to replace your car thermostat?


If you are struggling with all these questions or even one of these questions, then this is the right place for you.This article will educate you about everything related to your car thermostat, including what it is, how it works, when you need to change it, etc.

I too faced problems with my car thermostat a year ago. At that time, I didn’t know what to do and how to go about it. In fact, I didn’t even know if the problem was with the thermostat or with some other equipment in my car. This is when I searched for answers as to how to know if my car thermostat is at fault. And, when I finally found the solutions, I put them together in this article.

So, let us first know how a car thermostat looks like and how it works.

What is a Car Thermostat?

A car thermostat is a major component in the cooling system of a vehicle. It primarily has two functions. First is that it aids the engine to heat up to anoptimal temperature quickly. And, the second function is that it sustains an optimum temperature of the engine. Thus, the job of a thermostat is to regulate the coolant flow to the radiator that is air-cooled.

A car thermostat sits between the radiator and engine of the car. Mostly, the dimensions of a car thermostat vary between 2 inches and 5 inches in diameter.

Source: mechanics.stackexchange.com

With a car thermostat in your car that warms up the engine as quickly as possible, your engine has minimum deposits, wear off, and emissions. A perfect engine-operating temperature aids the engine oil to eradicate harmful deposits and lubricate proficiently. It also diminishes gas consumption and emissions, while contributing to the overall performance of the engine. Thus, a car thermostat has a great impact on the longevity and strength of the engine.

How does a Car Thermostat Function?

Image source: birdman308.com

A car thermostat blocks the coolant flow to the radiator until the car engine has heated up. This means owing to the car thermostat when the car engine is cold, the coolant does not go through the car engine.

However, as soon as the engine is warmed up at an optimum operating temperature, which is normally around 95 degrees C or 200 degrees F, the car thermostat opens. It is in a closed position when the engine is not heated up and sitting for some time.

A car thermostat is equipped with asmall chamber or cylinder that is situated on the device’s engine-side. This cylinder holds a wax pellet that melts and then inflates at a certain temperature, which is generally, 180 degrees F or 82 degrees C. It has a rod, which is linked to the valve and pushes into the wax.

When this max melts, the container expands extensively and thus shoves this rod out of the chamber, which causes the valve to open at the exceeding operating temperature. The wax composition determines the set operating temperature.

This, in turn,enables the hot coolant to flow through the car radiator and at the same time the water pump shoves the cooler-temperature coolant into the engine from the radiator. And, when the cooler-temperature coolant gets to the thermostat tank, contraction of the expanded fluid takes place while closing the valve of the thermostat.

Though the thermostat in reality never wholly opens or closes while the engine operates, it slowly does come close to either of these states in order to manage the flow of the coolant as per the engine’s operating status. This, in turn, facilitates the engine to function at an optimal temperature.

What Will Happen if the Car Thermostat is Faulty?

The car thermostat can stop working all of a sudden. And when it becomes defective, it can stop the engine to operate within an optimal temperature range and thus affect its overall performance.

  • In case the car thermostat is in a ‘stuck’ closed position, the coolant will not be circulated via the radiator and ultimately back via the engine, which can make the engine turn very hot steadily. And, if you fall short to notice this and still run your engine, within a few minutes your car’s engine will self-destruct.
  • Similarly, if the car thermostat is in a ‘stuck’ open position, the coolant will flow continuously, which will never heat up the temperature of the car’s engine and will result in performance issues. When the oil is at a lesser temperature, it will accelerate the wear of this component and thus will reduce the efficiency of the engine and increase emissions sooner or later.

No matter how the car thermostat gets stuck, it will severely damage the car engine. It is just that the amount of time will be different in each case.

How to Know if your Car Thermostat is Faulty?

When checking your car thermostat, you need to listen to your car’s cooling fan. This is an easy and quick way in order to know if the cooling system is efficient or not.

It is essential that you confirm the deterioration of your car thermostat. The hints for a faulty thermostat can be the same as the symptoms of a blocked radiator, a cooling system leakage, a faulty water pump, a deteriorated radiator hose, a botched radiator fan, a loose or worn out drive belt, or a low level of coolant.

Therefore, it is more vital to be sure if the thermostat in your car is acting up lately. No matter what is the failing state of the car engine, you can find it out through the different ways mentioned below.

One of the main things you will notice, if your car thermostat is defective, is that it will get stuck in either an opened or a closed position. It is significant that the closing and opening of the car thermostat is done at an appropriate time in order to maintain the right engine temperature.

If you find that the cooling fan operates even after a short drive or if the fan activates on a cold day, then there can be two possibilities; either the car coolant’s level has plummeted or the thermostat isn’t functioning properly.

The thermostat of a car is not effective in its functioning when you notice that your vehicle overheats shortly after you start the engine or when you see that the temperature gauge, located on the dashboard, hangs below or higher than its regular temperature mark or if it changes erratically.

Image source: carsdirect.com

If you don’t find any leakage in the cooling system of your car, then most probably the thermostat is at fault, which indicates replacing the thermostat. Additionally, if the coolant leaks near the housing of the thermostat or under the car, then also the thermostat can be failing.


Thus, the issues in the thermostat in a car can be easily diagnosed through the above-mentioned easy-to-follow troubleshooting procedures. They can be completed in a few minutes. These steps will let you know the reason behind the unusual operating temperature of your car’s engine.

Additionally, these methods will help you save your car’s engine from damage as well as save your money like they did for me.Hope that you like this article. If you have anything more to say about this topic, feel free to leave your comments below. Do share this article on various social media platforms.

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