Car keeps overheating? Why A Bad Thermostat Is The Cause.

A thermostat is a fundamental component of a car. It’s through a thermostat that the flow of hot water is controlled through the radiator.

If the component gets damaged or goes bad, you can expect many problems such as temperature fluctuations, leakages, and more.

But will thermostat cause overheating? We’ll drive in-depth about the consequences of a bad thermostat and whether or not it can be fixed.

How Does a Car Thermostat Work?

But before we begin, how exactly does a thermostat in a car work? 

A thermostat is responsible for managing the engine temperature. It ensures that the average temperature of a car engine stays within the acceptable range of 195-220°F.

It acts as one of the main components which determine how hot or cold the engine can get, acting as the backbone of the car’s cooling system.

If the car overheats, the thermostat responds by opening and allowing the engine coolant to reach the radiator where it can get cooled down.

In its essence, a thermostat acts as a valve between the engine and the radiator, controlling the flow of the coolant based on the need of the car.

So, how exactly does the thermostat understand when to open and close?

It’s simple, a thermostat comes equipped with a type of wax that doubles as an expanding agent. The wax reacts when the coolant reaches a specific temperature, causing it to expand and open.

How Does a Car React to A Bad Thermostat?

If you have a faulty thermostat, you can expect several problems with your car’s performance. One of the obvious problems is poor engine performance.

The engine will have no mechanism to counteract extreme temperatures. It will be struggling to perform, leading to a poor driving experience as well as a fall in fuel economy.

Worst of all, your car will be vulnerable to over and under heating.

As mentioned before, the thermostat acts as one of the primary mechanisms for the temperature control system in place within most cars.

With a bad thermostat, you can expect your car’s temperature to be far out the acceptable margin.

Not only would the engine’s efficiency be affected, but if gone unresolved for a long period, it can result in serious damage to your engine.

Other issues from a bad thermostat that you could expect are related to experiencing fluctuating engine temperature, and coolant leaks.

Testing Your Car Thermostat

If everything sounds too complicated, then rest assured, checking whether your thermostat works or not is a fairly simple and easy process. All you have to do is to let the engine stay idle for a few minutes after starting it.

Now, carefully remove the radiator cap to see whether the coolant is flowing or not.

Remember, the coolant is only supposed to pass into the radiator after the temperature inside the engine surpasses a specific temperature. The engine overheating within a few minutes of starting up is impossible.

So, if you see the coolant flowing inside the radiator, it’s a clear sign that the thermostat is most likely stuck or faulty.

Other Common Reasons Why Your Car Might Overheat

If you’re facing consistent problems with an overheating engine, you should also know that a bad thermostat isn’t the only possible reason behind your troubles. There are several reasons why your car might be experiencing overheating.

The following are some of the common culprits.

Inadequate Quantity of Coolant

The coolant is the liquid through which the temperate of the engine can be maintained. It’s the main backbone of cooling systems in cars.

The qualities of a coolant allow it to absorb heat. It moves towards the radiator and the coolant temperature is brought down.

You might not be using enough coolant as recommended by the car’s manufacturer.

You can fix this issue by regularly checking whether the coolant levels have dripped or not.

Doing so will barely take five minutes, but it will save you a lot of trouble in the future as your cooling system will be maintained.

Damaged Radiator Fan and Cap

Up to now, the thermostat and the radiator have been mentioned which work together to control the engine’s temperature.

The reason why your car might be overheating can be related to both of these components. If the radiator has gotten damaged in any way, its functionality can be compromised.

Moreover, the radiator also has specific components that can be damaged.

Such as the radiator cap, which works to keep the system pressurized, and the radiator fan, which helps remove the hot air.

Blown Head Gasket

The main purpose of a head gasket is to keep the engine and cylinder block separate.

A blown head gasket creates a high possibility that the coolant could flow into the combustion chamber and allow engine oil to leak into the cooling system. This results in your car overheating.

Fixing Your Car’s Thermostat

Once you have identified that the fault lies in your thermostat only, it’s time to fix it or rather, replace it. Despite how essential thermostats are, you can find them easily in the market at a relatively cheap price.

The following are some of the things you should have at hand before starting.

Step 1: Locate and Remove the Old Thermostat

The first step is the most obvious one, you need to identify where the old thermostat is. Usually, you’ll find it on top of the engine. That’s near the area where the radiator hose joins the engine.

Remove the bolts that hood the radiator hose and after that remove the thermostat. Some coolant will most likely leak as you follow this step.

To save yourself from creating a mess, remember to place a bucket or container underneath your work area.

Once you have removed the old thermostat and the gasket that is included with it, you should compare it with the new replacement. Everything about the new thermostat should be the same as the one your car had equipped.

Step 2: Cleaning

Before doing anything else, use a plastic scraper to remove any residual sealing compound and pieces of the old gasket. You should also clean the engine and the radiator hose before drying the surface with some rags.

Step 3: Install the Thermostat

The next step is fairly straightforward.

Use an RTV sealant if you don’t have an adhesive gasket, and install the thermostat by first placing the gasket and dropping the thermostat with the spring side down.

Hold the thermostat in place to allow the adhesive to stick. Reinstall the radiator hose once again as it was before, refill the coolant formula, and voila! You’re done!

Frequently Asked Questions

Can A Bad Thermostat Cause the Engine to Overheat?

The simple answer to this question is yes, it can. A bad thermostat is one of the most common reasons behind your engine overheating. The main purpose of a thermostat is to monitor the temperature of the engine.

The valve is triggered to open once the engine crosses a specific temperature and works on reducing the heat.

If you have a bad thermostat, however, you have no counter against rising temperatures. Imagine you’re stuck in your house during summers as the house gets too hot.

You can’t open the windows, use the ac on or even turn the fan on. That’s exactly what’s happening to your engine once your thermostat stops working.

What Are the Possible Reasons for A Thermostat to Stop Working?

There are several possible reasons why your thermostat might not be working properly.

This can be due to a bad water pump or a leakage in the system. Other reasons could also include a collapsed radiator hose and a loose water pump.

You can avoid any serious problems by regularly checking and cleaning the thermostat for buildup.

Can I Use Any Thermostat for My Car?

No! Be careful to use the exact thermostat that has been designed for your car and model.

That’s because using a thermostat with different calibrations might create more problems for your engine, such as overheating or running too cold.


A bad thermostat can cause several issues while you drive your car. One of the most common symptoms of a faulty thermostat is your car overheating.

However, there can be other reasons causing your engine to overheat. Problems with the radiator or the gasket can also disrupt the cooling system of your car.

You can easily follow the previously mentioned steps to check whether your thermostat is working or not. While you can fix a faulty thermostat, it is much better to replace it.


Dean Alvarez, TireForge Head Author

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