How To Unstick A Thermostat In A Car: Top Best Tips

How to unstick a thermostat in a car? Avoiding car overheating issues

A thermostat is a vital component of a car’s cooling system that adjusts coolant flow and coolant temperature, so its fault causes an extremely hot engine that leads to serious damage and the faulty thermostat should be removed.

If you do not know how to unstick a thermostat in a car, we try to give you tips on how to succeed and how to detect the reason for a bad thermostat.

What is a car’s thermostat?

The thermostat housing is the place where a car thermostat is hidden. It is a small but essential component of the engine cooling system, you may find it where the upper radiator hose is attached to the engine block. It may be located near the coolant fluid tank.

A thermostat controls coolant flow and is responsible for closing it under the specified level in case the temperature is low. It is a kind of engine temperature gauge that indicates on your dashboard when the temperature rises or falls in a car engine.

While operating, the engine thermostat is responsible for opening the thermostat valve allowing the coolant liquid to enter the cooler in case the operating temperature is higher than it should be, above the specified level.

When you start a vehicle that is working properly, the engine temperature increases, stabilizing the temperature gauge and ensuring fuel consumption, and preventing any environmental pollution.

What is the function of the engine thermostat?

There are many types of temperature gauge devices. The thermostat on your vehicle only regulates the heating temperature.

Contrary to the domestic thermostat, where the temperature is not adjusted. This thermostat is designed after an outlet in your bathtub. The valve opens, allowing fluids to pass through the circulating radiator. This liquid is coolant. It absorbs energy and moves it quickly.

In case the engine overheats, the car’s engine is impacted to serious damage.

During cold temperatures, however, coolant flows less effectively. Also, the motor needs constant temperatures and the thermostat is essential. A malfunctioning thermostat cannot control airflow properly.

Coolant cools the engine down as expected. When it is opened, cooler water is flowing in, causing evaporation of heat, which lowers engine temperature. Once the thermostat is stuck open, the coolant remains unaffected as the engine warms up.

What may happen when a thermostat is stuck?

It was mentioned above that when a car thermostat sticks, it may lead to severe problems with a faulty engine. There are possible troubles when the thermostat is stuck or the coolant leaks.

Coolant leakage

Before blaming the stuck thermostat, have a look at the HVAC (heater core and automatic conditioning) whether it is working properly. In case there are no coolant leaks from the thermostat, then HVAC causes a problem.

A faulty heater core might also cause the absence of warm air coming from a heater.

Before starting the car and allowing the engine to idle, check the radiator cap. Open the car’s bonnet and remove the radiator cap to see if there is any liquid allocated to the engine. Noticing coolant leaks out means that the thermostat is stuck.

If the coolant fluid leaks around the thermostat housing, it requires replacement as a metal cover cannot be repaired, only changed.

In case there is no leakage, start the car and wait for about 10-20 minutes until the car engine cooling system is warm enough to show the appropriate temperature. If there is still no fluid, but the temperature gauge rises, such issues may be caused by a valve.

A thermostat stuck closed

When the thermostat is stuck in a closed position, it leads to serious problems with your engine. Coolant flow is disrupted, and coolant liquid cannot get through the radiator hose to cool it, causing the engine to overheat.

In this case, the car engine heats as it cannot be cooled down without any cooling help. Within time, the hot engine will increase the temperature, heating the coolant thermostat and leading to car overheating.

Various symptoms come with a stuck closed thermostat. Not normally cool engine temperature indicating too much coolant leaving the system causes engine overheating troubles. You might face a car overheating, which also influences fuel consumption.

If you suspect the vehicle’s thermostat is stuck closed, you should wait for about 10 – 20 minutes while your engine heats up to a proper temperature that will be seen on a temperature gauge.

Check the engine temp and the upper hose after 20 minutes. As soon as the temp gauge indicates the normal temperature, the coolant flows as it should cool the engine.

If the hose is colder than the engine, it means that coolant doesn’t go through it. In case the upper radiator hose is hot, and the lower hose is cold, this also indicates a thermostat problem.

Coolant leaking is another problem caused by a bad thermostat. The faulty thermostat won’t allow coolant to flow, been trapped in the closed position.

How can you avoid a thermostat stuck closed?

Dirty engine oil can cause the thermostat to become stuck closed, avoiding coolant liquid from proper circulation.

We strongly recommend measuring regularly your engine oil level with a dipstick when a car is cold. In case the amount of liquid is not enough, it should be poured.

Additionally, the filter should also be checked in case you are aware of problems. If there is dirt build-up on a filter, the oil filter should be changed without changing the oil, though changing the oil is recommended with an oil filter.

A thermostat stuck open

When the car is cold, and you start it, the thermostat is closed, only allowing cooling fluid to get through the engine and the heater core in case the heater is on. If the problem is not with a plugged heater core, the overheating issues might be caused by an open thermostat.

The most common reason for a stuck open thermostat is corrosion. Within time, the corrosion can become bigger and avoid the appropriate opening of a thermostat.

When a thermostat is stuck open, it means there is no possibility to accumulate the coolant level. In this case, the engine warms with difficulties. Without proper warming, the engine temperature is also low, and this leads to a car idling in cold air conditions.

The common issue with a bad thermostat is that the temperature gauge indicates various numbers, approximately 220 – 230 degrees Fahrenheit.

Avoid operating your vehicle when you notice a car’s thermostat is stuck open. Thermostat replacement is the only possible solution in this case.

How Can You avoid a stuck open thermostat?

When the thermostat is stuck open, you can avoid this issue by flushing your cooling system components regularly. Such washing will remove any built-up corrosion and debris which might lead to a malfunctioning thermostat.

Besides, every time you pour new coolant, ensure it is fresh and of good quality to flush the cooling components.

How to fix a stuck open thermostat

If the problem of a stuck open thermostat is detected while driving, as the temperature rises, you should immediately stop the vehicle to avoid engine damage. Leave the car on a flat surface and switch it off, allowing the engine to cool down.

Observe the thermostat itself, remove the radiator cap, and after that, you may disconnect the radiator hoses from the motor. Ensure they are not hot. Replace the thermostat valves.

Pour more antifreeze if it is needed and try to run the vehicle. If the problem continues and the temperature rises, in this case, the thermostat replacement is unavoided.

How to detect a stuck thermostat?

The thermostat stuck closed issue can be fixed by removing the radiator cap or opening the car’s bonnet.

The coolant should be flowing in an open thermostat without the engine leaking. The cooling system does not run while the engine overheating. If the thermostat is in a closed position, it should start flowing within 10-15 minutes. Difficulties in warming the engine cause the stuck closed thermostat.

What are the signs of a bad thermostat?

Difficulties with heating issues such as slow coolant flow or a car overheating signed by a heat gauge are mostly caused by a stuck thermostat. But unfortunately, these are not the only troubles you may face when the thermostat is stuck open or in a stuck closed position.

In any case, it is difficult to open.

If you experience extremely high temperatures in the engine, but the issue is not with a thermostat, in this case, you should check the leakage of cooling, or it might be a problem with a water pump. It is also essential to fit a pump to detect the heating issue.

Regular overheating because of a lack of fluid to cool the engine may sign a faulty water pump. To solve this issue, you might need the water pump replacement.

What causes the thermostat to stick?

The thermostat is an element responsible for the distribution of coolant within the engine to keep the operating temperature steady.

Too much coolant might lead to a closed thermostat. To avoid it, regularly check the coolant level. Heat can be caused by extreme temperatures.

Other common reasons for faulty thermostats are blocked heating radiator hoses, incorrect cooling levels, fan systems, low levels of water, or problems with a water pump.

What is the operating temperature of a thermostat?

The appropriate operating temperature in the car thermostat is approximately 120 °F.

For a proper temperature gauge, coolant has to be sensitive to engine conditions: hot and cold. Engine thermostats are responsible for either opened or closed positions.

Usually, when coolant is open, it reduces the power output and is pushed out until the engine gets warm. The temperature of the heater doesn’t rise as the thermostat controls coolant flow and its temperature.

How do I know if my thermostat stuck open or closed?

The appearance of a “check engine light” is the most common sign of a problem with an erratic temperature gauge engine temperature. To avoid the mechanic’s visit, you might troubleshoot yourself and find the best solution.

If your motor vehicle’s thermostat has blown over the temperature, you will face a stuck thermostat while driving.

In case the coolant doesn’t circulate correctly, this causes high engine temperatures and a car overheats. The thermostat should be replaced.

When the car runs warm, keeping the same temperature, it may cause closing the temperature gauge down.

If case the cooling agent is circulating but not sufficiently, it causes problems in cooling the engine. The thermostat replacement is also required.

Can a stuck thermostat fix itself?

A thermostat might provide incorrect work in case it is damaged.

The best variant is to replace the thermostat valve and attach a new thermostat. Another way of fixing valves is to restore them to their starting positions, though this is temporary. If it was the first solution, ensure the thermostat is free of any coolants that could interfere with its performance.

Can you drive with a bad thermostat?

Yes, you can drive with a bad coolant thermostat. The thermostat is the device used for controlling how much coolant comes into the engine for cooling and is usually used for cooling in automobile engines.

The thermostat provides the engine with optimal working temperature when opening/closing a valve that enables coolant flows. Depending on the engine temperature that is known by the temperature sensor, the thermostat closes the cooling fan and prevents the cooling.

When a thermostat is locked open, it circulates continuously without causing any heating. It causes engine overheating, leading to serious damage. If the vehicle is overheated when it stops working, in this case, apply an emergency brake, and a stop is required.

Turn off the engine, open the car’s bonnet and let the cold air get in for at least some cooling while warm air gets out. Never open the coolant cap while the engine is hot to avoid burning.

Leave the car on a flat surface and allow the engine to rest while cooling. The cooling of the motor is important to reduce further damage to the vehicle. It may take you at least 10 minutes, depending on the outside temperature, to lower the engine’s temperature and keep running until you can repair the damage.

Can you drive a car without a thermostat?

No, there is no possibility to run a vehicle without a thermostat. The temperature controls the cooling fluid in an automobile, and without it, the motor can overheat, and your trip won’t last long but will cost you much.

How to replace a stuck thermostat in a car?

Most thermostat repairs and replacements require replacement parts. The process is simple and cheap. All that you need for avoiding the problem with a stuck thermostat is a new thermostat installed in the car.

Install a new thermostat

As soon as the check engine light in your vehicle appeared, you should open the bonnet and check the condition of the thermostat. You may find it in a thermostat housing, where the engine is connected to the upper radiator hose. If you cannot easily get away from those small parts, it means that the thermostat is stuck open. You should take it away and put in a new one.

Installation is as simple as removing an oven from evaporator holes. It will spin freely, and it might not look snug. First, remove the thermostat housing. In case the housing is also damaged, it should also be replaced.

The thermostat housing in your vehicle looks like a small metal piece linked to your engine block with thermostat hoses. You need a socket wrench to loosen the bolts on the housing and keep them from not losing. Tightly pull the thermostat housing off the motor to access the thermostat itself.

Clean the interface surfaces

Before replacing the thermostat, you must ensure the mounting surface is clean. This area gets dirty and greasy during the ride. When this surface interferes with coolant leaks or moisture is introduced to the housing.

Corrosion is the reason for the thermostat cracking or stuck. I use razor blades for cleaning both surfaces, then an office towel to clean the interface surfaces. It is possible to use smaller angle grinders that have a thick pad on them to obtain more accurate results.

Please avoid the removal of any wires or tubes that may be in contact with the cleaning process.

Drain the coolant

During the process, you will expose the coolant lines. They should be removed when you push the gas pedal, such lines might allow the coolant to flow. Releasing the pedal, it stops leaking and heats up again. To avoid annoying cleaning and further damage, coolant lines should be cleaned.

You may use Lumax LX-1632 Black 15 Quart Drainmaster Oil Drain Pan to drain off all coolant.

Hop beneath the vehicle for better access, or use DIY ramps on cars. Find coolant lines and see the bolts that are attached to the connectors. They are on the back side near the radiators. Set up a bucket under your vehicle. Unscrew the drain plug, allowing the coolant to pour out until the radiator is empty.

Remove the thermostat

The thermostat has a metal component inside after removal. Try to avoid touching this element, you may start photographing all elements to keep track of and remember their direction.

There are several ways to turn thermostats in reverse, and you probably wouldn’t do it at all. Try removing it by using your finger. Please take great care when handling it. Moreover, you can see the current thermostat condition. It is controlled by a magnet that rotates the thermostat head in certain conditions.

Reinstall the housing

Speaking of housing, we need to get this fixed up again. Always use a bolt in the correct hole for secure installation. If you install this device, your thermostat could fall apart. It’s very easily solved by just checking before putting the tubes in place.

After you tighten all the bolts, ensure they are firmly screwed. Take a minute to examine a pipe hole inside the housing. Keep an eye on the thermostat before proceeding.

Put a new gasket on

A gasket is necessary before replacing the thermostat. It would help if you had research to get exactly what fits your vehicle, but they can usually be purchased with replacement housing.

Check the holes for mounting to the hole in the gasket before gluing. Push the seal in tightly and wait until it sets.

Can a car overheat without a faulty thermostat?

Yes, the car overheats in case of faulty pumps, hoses, and fans. Several issues may cause high temp and make your engine overheat.


What happens when a thermostat is stuck closed?

In cases where a thermostat is closed, the coolant is blocked and doesn’t pass through a cooling chamber, leading to the motor overheating.

Can I drive my car if the thermostat is stuck?

You can drive, but you’d better avoid running the vehicle, as it might result in serious damage to the engine.

How do you free a sticking thermostat?

Stop the car and let the engine cool down. Locate the thermostat, it is near the coolant fluid tank and the car engine. Disconnect the hoses from the engine, replace the valve, and then the sticking thermostat.

What are the symptoms of a stuck thermostat?

The most common sign is a motor overheating and a thermostat that isn’t easily opened or closed.


We observed the most common causes of a bad thermostat and outlined how to unstick a thermostat in a car. It is not a complicated procedure and with some tools and knowledge, you might easily cover this issue by yourself.

To detect the problem with a stuck thermostat, you should check the pump and radiator hoses, the heater core issues, and the fan to ensure that a thermostat needs replacement.

To avoid costly engine repair, we advise you regularly check all the liquids in your car, and in case a thermostat is stuck, replace it immediately.

Read also: Car Overheating Then Going Back To Normal – 7 Reasons

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