Thermostat stuck closed symptoms.

Thermostat stuck closed symptoms will lead to no coolant flow which causes overheated engine damage amongst other complications.

A closed thermostat has negative impact on the vehicle’s performance. Ignoring the situation affects the car’s cooling system which can lead to significant issues and potential damage.

When the thermostat valve doesn’t open, it prevents coolant from flowing through the engine. Therefore, this disrupts the balance of temperature regulation, leading to overheating and potential engine damage.

However, a thermostat that’s functioning properly allows coolant to flow freely when necessary. Hence ensuring optimal engine performance.

Car owners need insight into the symptoms of a bad thermostat in order to identify potential issues early on.

Therefore, they can take appropriate actions to prevent further complications.

Stuck closed thermostat symptoms.

The opposite effect on coolant flow of a stuck open thermostat is a the effect of a closed one. Whereby, the open one allows continuous coolant flow while the closed one completely restricts the coolant flow.

The engine struggles to reach optimal operating temperature when the thermostat valve is stuck open. However, when its closed, it prevents engine temperature levels from lowering to a normal level.

There is more likely-hood of an engine overheating when the thermostat is shut than when it’s open.

1). Overheating engine.

An overheated engine is the most common symptoms of a thermostat stuck closed. Coolant cannot flow through the radiator when the thermostat fails to open.

Therefore, the engine struggles to cool down because the cooling system is ineffective. As a result, the temperature inside the engine continues to rise, leading to overheating.

2). Lack of heat from car’s heater.

There are occasions when the AC does not blow cold air during hot weather and other occasions it fails to blow hot air in cold weather.

The effectiveness of the heating ventilation and air conditioning (HVAC) system depends on a fully functional cooling system.

when there is no heat coming from the car’s heater, it means something is wrong with the engine temperature level.

Warm air goes into the cabin from the heater core. The thermostat regulates the flow of coolant through the heater core.

The coolant that flows to the heater core is of high temperature. Therefore, it doesn’t reach the heater core if the thermostat is closed.

Hence resulting in a lack of heat during the cold weather conditions.

3). High temperature gauge reading.

High temperature gauge readings are also referred to as staying in red zone. A stuck closed thermostat causes the temperature gauge on your dashboard to read high levels.

In this situation there is no proper circulation of coolant. Hence causing the engine to operate at higher temperatures than normal.

The excess heat that builds up within the engine is shown on the dashboard by the temperature gauge. At first when you start the engine it will run hot without overheating for while.

As a result, your temperature gauge may indicate abnormally high readings or even reach dangerous levels.

4). Check engine light.

Dashboard warning lights are programmed into the vehicle on board computer to show when there is an issue.

There are engine temperature sensors that trigger the check engine light whenever the thermostat valve is stuck closed or open.

The engine control module (ECM) uses different types of car sensors to detect the abnormal occurrences. For example, abnormally high engine temperature.

5). Reduced power and performance.

Engine power output depends on the presence of the optimal operation temperature. This is the type of temperature that optimizes the combustion process by ensuring a proper fuel air mixture ratio.

One of the main reasons for reduced engine power is an overheated engine. The engine temperature level at this point is just not conducive for the combustion process.

Therefore hindering vehicle performance whereby you notice that its movement is sluggish. Additionally, the engine may start to misfire or operate less efficiently.

6). Coolant overflow.

Coolant is an essential part of the measures put in place by manufacturers towards engine temperature control.

When the thermostat is stuck closed, coolant doesn’t flow through the engine. Therefore, a lot of it remains around the radiator.

The radiator cap is equipped with a pressure release valve meant to regulate the amount of coolant pressure.

When engine temperature rises, coolant temperatures also increase and this causes an increase in pressure level.

The thermostat should open to allow the coolant to go to the radiator overflow plate. Where pressure relive happens and heat dissipation starts to takes place.

Therefore, if thermostat doesn’t open, this will not be possible. Hence causing coolant pressure build up inside the radiator.

Which causes the radiator cap to start leaking coolant. Eventually causing the engine to suffer an incident of overheating.

Thermostat stuck closed quick fix.

Thermostat in a car

You can try to DIY the task of fixing the thermostat. However, you have to be aware of where the thermostat is located within your vehicle cooling system.

When the vehicle starts to experience the thermostat stuck closed symptoms, there are a few things you can do to fix them.

Follow the instructions found within the owners manual while undertaking these fixes. Afterwards, you can seek professional help.

Here are some steps to address the issue:

1. Flush the cooling system.

Coolant flush is a car maintenance activity that you need to perform on a mileage based or time based occasion. The coolant flush involves;

  • Removing old coolant.
  • Cleaning the cooling system.
  • Refilling cooling system with new coolant.

Old coolant surfers degradation over time which compromises its ability to regulate the engine temperatures.

Degradation takes place based on the time factor. Whereby the coolant surfers from the effect of exposure to heat, intrusive elements, debris and corrosion.

Cleaning the cooling system involves the use of specialized products or water. They remove any corrosion and contaminants found in the cooling system.

Hence leaving a clean environment that is ready for the new coolant refill. Purchase the coolant that’s specifically recommended for your vehicle engine.

Anything that may be causing the thermostat to get stuck closed is removed during the act of flushing the cooling system. For example, blockages or debris.

Following these simple steps flushes the cooling system.

  • Drain the coolant from the radiator.
  • Use a flush solution and follow the instructions provided by your vehicles manufacturer or on the container of the flush solution.
  • Refill the system with fresh coolant.

2. Replace the thermostat.

If you’re still experiencing symptoms of a stuck closed thermostat even after flushing the coolant, the problem is with the thermostat itself.

In order to resolve the problem, you will have to deal with the faulty thermostat. Consider replacing it with a new one.

If you’re not familiar with the process through which this activity takes place, ensure that you follow your owners manual to learn.

Additionally, you can just consult a professional mechanic who will help you to resolve this problem. This is the process you need to follow in order to replace the thermostat with a new one.

a). Thermostat housing.

The thermostat housing is the first thing you need to locate. Most manufacturers place the thermostat housing within the radiators top hose.

However, this varies from vehicle design to the next. It is mostly connected to the engine block.

b). Access and remove the thermostat.

Remove the hose connectors from the radiator. Place a container under the radiator to allow the coolant that flows out from the radiator to be caught without draining to the ground.

Allow some small amounts of coolant to flow out. Enough amounts to be able to locate the thermostat.

Once you have access to the thermostat, remove the screws that hold it in place to loosen its connection to the engine. Afterwards, pull the thermostat from its location to remove it.

c). Examine and replace the old thermostat.

Once you have removed the thermostat, examine it for a chance to see if you can repair it. If there is no chance of repairing, dispose of the old thermostat responsibly.

Get a new one and install it in place of the old thermostat. Ensure that it is fastened in place so that it does not come off when coolant runs through it.

Restore everything in the cooling system.

3. Check and replace other related components.

When other components of the cooling system are faulty, they could cause harm to the thermostat. For example, faulty water pump which pushes coolant.

Check for any signs of damage or wear on the radiator cap and replace it if needed. Inspect the water pump for coolant leaks or malfunctioning.

Ensure that you account for the task of inspecting the cooling system components within your car maintenance schedule.

How to unstick a thermostat in a car.

You can restore the functionality of a thermostat by unsticking it yourself. However, for you to proceed with this process, you will have to start with accessing the thermostat and removing it.

Tap the thermostat housing gently.

This is the most basic method of solving a stuck valve. Gently tapping on the thermostat housing will free up the stuck valve.

This action of tapping will dislodge what is causing the thermostat valve to stick closed. For example, debris or corrosion.

Warm up and cool down the engine multiple times.

To ensure the engine reaches its optimal temperature, make sure it runs for a few minutes. Observe the temperature gauge and once it has reached normal operating temperature, let it run for a while.

This allows coolant to circulate through out the system from the overflow reservoir and radiator. Next, turn off the engine and let it cool down completely.

Repeat this process of warming up and cooling down the engine several times. This will allow the thermostat valve to experience consecutive expansion and contraction.

Hence, opening up to allow smooth flow of coolant through out the system.

Manually open the thermostat if possible.

After removing the thermostat from its housing, check if there is any visible obstruction or damage. This could be what is causing it to stick closed. You can use your hands or the appropriate tools to manually open the thermostat.

Once its open you can perform a thermostat test to check whether it responds to changes in temperature by opening and closing as it should.

You can attempt to unstick a closed thermostat but this is just a temporary fix. Consult a professional if you are not sure about any aspect of this process.

Exercise caution when working with your vehicle’s cooling system.

Testing if the engine thermostat is stuck.

Thermostat testing determines whether everything is working well. To determine whether your engine thermostat is stuck closed, there are a few simple tests you can perform.

  • Boiled water test,
  • Multimeter test.
  • Visual examination test.

By following these steps, you’ll be able to diagnose the issue and take appropriate action.

1. Using an infrared thermometer.

You can use an infrared thermometer to test for a stuck thermostat. The infrared thermometer can show you the measurement of temperature variations across different parts of the engine.

Pay close attention to temperature measurement of the areas near the thermostat housing and the radiator hoses.

Significantly different temperature readings in those areas could indicate a problem with the thermostat.

2. Monitoring coolant flow.

Secondly, in order to determine whether your thermostat is stuck, you can monitor coolant flow. Buildup within the cooling system components tends to be one of the hinderances of coolant flow.

For example, radiator hoses. You need to monitor coolant flow through hoses while observing changes in engine temperature.

Start the engine and let it run idle until it reaches normal operating temperature. This is the point when coolant starts circulating.

Afterwards, carefully touch each radiator hose to check for any noticeable changes in temperature. This is effective because the coolant will already be circulating.

If the hose is cold or cool this may suggest that the thermostat is stuck closed.

3. Conducting a resistance test.

Thermostat terminals in a car

This test will involve the use of a specialized instrument called the multimeter. Ensure that your multimeter setting is at the ohm resistance measure.

Hence allowing you to conduct a resistance test on the thermostat sensor. Disconnect the car battery and remove the sensor from its housing.

Connect the leads of the device to both terminals of the sensor. Obtain the readings and compare them against manufacturer specifications.

This will help you to determine if the thermostat is functioning correctly. These tests will help you to identify potential issues with a stuck closed thermostat in your engine.

follow safety precautions when working with engine heat dissipation systems. Additionally, consult a professional when necessary.


We have a comprehensive understanding of thermostat failure symptoms from the information above. For example, increased fuel consumption, coolant loss, irregular operating temperatures, unusual engine noises.

Additionally, there is a conclusive understanding of the potential causes behind thermostat failure. Address these issues promptly to prevent further damage to your vehicle’s engine.

Solutions for a stuck closed thermostat, can be some quick fixes or attempts towards unsticking it. Consult a professional mechanic for assistance where you’re unsure or uncomfortable with performing these tasks.

To prolong the lifespan of your car’s cooling system, you need to perform

From these symptoms can indicate a thermostat stuck closed. It is crucial to regular maintenance and timely repairs.

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