Radiator Thermostat Stuck Closed – Can It Fix Itself?

If your car thermostat is stuck, you should know you have a big problem. The reason is that the thermostat is a significant feature in your car’s cooling system for engine performance.

Thus, if this feature is “stuck,” your engine is affected.

Find out in this article what you can do when your thermostat is stuck and anything else important for you to know.

What causes the thermostat to stick?

The thermostat is a component responsible for distributing an even amount of coolants within the engine, to keep the operating temperature at a decent level – it shouldn’t get too high or too low.

If any of these situations happen, i.e., too much coolant or too little, then you could definitely have a stuck thermostat.

It often comes with your car overheating.

Other reasons why you could have a bad thermostat include a blocked radiator, a poor or inactive cooling system (or fan), and a low water level.

What is the operating temperature of a thermostat?

The ideal operating temperature of a car thermostat is between 180-degrees Fahrenheit and 212-degrees Fahrenheit.

To achieve the right temperature gauge, the coolant must respond to the condition of the engine, i.e., warm or cold.

The engine thermostat can operate either in an open or closed position. If it is open, then the coolant lowers engine temperature; on the other hand, if it is closed, the coolant stays blocked until the engine is on the warm side.

Since the thermostat controls coolant flow, the radiator is safe – the coolant only gets to the radiator when it is hot.

How do I know if my thermostat is stuck?

If you suspect a thermostat problem, you can try to remove the radiator cap and expose the engine.

Two things are likely to happen:

If you have a stuck open thermostat, the coolant should flow immediately without the engine overheating.

However, if you have a stuck closed thermostat, the coolant won’t flow until your engine warms properly.

If your thermostat is stuck closed, the coolant should begin to flow after 10 to 20 minutes until your engine heats up to a normal temperature.

The warming of your engine when your thermostat is in a closed position is mainly because the coolant isn’t getting to the radiator. And it isn’t news that coolant not reaching the radiator could cause an engine to overheat.

What are the signs of a stuck thermostat?

There are different signs or symptoms that come with a stuck open or stuck closed thermostat. They include:

  • You could have an abnormally cool engine, which literally means too much coolant is leaving the system. If that happens, you will likely experience engine overheating issues.
  • If you experience a car overheating, there is also a good chance it affects fuel consumption. At this point you have a reduced fuel economy because you have a hot engine.
  • You may also discover your air conditioning or heating system has problems – for instance, your heater may not produce warm air because the plugged heater core is faulty.

What are the signs of a bad thermostat?

Apart from the plugged heater core problems and overheating issues because your thermostat is stuck open, you can experience other things. With the following, you should be able to tell if you have a bad thermostat or not.

  • The “check engine” light gives a warning.
  • Temperature gauge reads high – stays on “cold.”
  • The engine has its temperature changing erratically.
  • Constant coolant leaks underneath the vehicle or around the thermostat housing.

How Do You Know If There Is a Problem With Your Water Pump?

As aforementioned, you could have a faulty thermostat because of your water pump. That means, it is important to always check if your water pump is failing or not.

Here are some signs of a failing water pump:

  • Constant overheating because there is not enough fluid to cool the engine.
  • Consistent coolant leaks
  • Corrosion on the water pump
  • Loud noise from the water pump area

Can a stuck thermostat fix itself?

It may be almost impossible for a car’s thermostat to fix itself back to normal.

However, what you could do as a car owner is to replace the valves in the thermostat with new sets.

Another thing you could do is fix the valves back to their initial positions but this solution is only temporary.

If you would go for the first solution, you should make sure the radiator hose doesn’t show coolant hindrance; instead, it should ensure easy movement/flow for the thermostat’s overall performance.

How to fix a stuck thermostat?

If you want to fix a stuck thermostat in a closed position or an open position, here is what you can do to set the engine back to normal temperature as coolant flows.

Step 1: Get Your Car Ready

When you see a “check engine” light, you know it’s that time to check your thermostat if it is stuck or faulty.

What you need to do first is prepare your car – park in a very good spot (preferably, a flat surface) and keep the emergency brake on.

Then, make sure your car cools down properly – you might have to wait for a few hours or overnight after driving to keep the engine’s temperature low.

Step 2: Locate the Thermostat

The next part is popping your car hood open and locating the thermostat housing. Most cars have their thermostat housing close to the coolant fluid tank or engine.

Step 3: Remove the Radiator Cap

Once you’ve found the thermostat housing, you should remove the radiator cap so you can reach the thermostat easily.

It is important that you are carefully doing this – at no point should you have the thermostat open when the car is still on because you could experience a sudden burst of coolant.

Step 4: Work on the Thermostat Hoses

Once the thermostat opens, you should see other features like the thermostat hose.

Before you do anything else on the thermostat, you should check out the coolant flow in the engine as well as the temperature – you can do this by starting the cap. However, you should keep a safe distance while at it.

After the engine reaches a specific temperature, you can now check the thermostat hoses.

If the upper radiator hose is hotter than the lower one, then the thermostat is stuck; however, if it is the other way around, it is still good.

Step 5: Change the Valves in the Hoses

If you happen to have a stuck open thermostat, then you need to change or reposition the valves in the hoses.

The valves are the actual reason why the thermostat is stuck.

Step 6: Replace the Thermostat

If the valves are now in the right condition, with no sign of coolant blockage or hindrance, you can replace your thermostat back to its original position.

You may also have a situation where the thermostat could get stuck past halfway.

It could be as a result of the piston rods getting jammed or degrading. You can replace them and fix the thermostat back.

Can you drive a car with a stuck thermostat?

It depends on if the thermostat is stuck open or in a closed position.

Can you drive with the thermostat stuck open?

Yes, you can drive a car with the thermostat stuck open. However, you cannot drive for long because the engine temperature drops and becomes cold and eventually runs out of power until it is damaged.

Can you drive with the thermostat stuck closed?

No, you cannot with the thermostat stuck closed.

The reason is because engine temperature increases, causing car overheating. It becomes an immediate problem for mobility.

Frequently Asked Questions


No, a stuck thermostat cannot fix itself. 

Whether your thermostat is stuck open or closed, or you are experiencing a coolant leak or not, you should always invest in the maintenance of your engine and car’s cooling system.

You know you need a new thermostat when the temperature gauge is unusual, especially when it could cause a car to overheat.

Check if you have a stuck or bad thermostat today and get it fixed before it ruins your engine’s life.


Dean Alvarez, TireForge Head Author

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