How To Unstick A Thermostat In A Car? 9 Detailed Steps! (2023)

A closed thermostat can lead to many awful problems for your car. The most terrible one is that the flow of coolant can’t pass the radiator and can make your engine temperature really high.

In this case, it’s time for you to unstick a bad thermostat. But how to unstick a thermostat in a car?

Don’t worry if you don’t know where and how to start, as we’re here to help you with that. This article will guide you on how to fix a stuck thermostat.

I’ll give you in-depth information about this troubleshooting process and a step-by-step guide to displacing a bad thermostat in your vehicle.

What Does The Thermostat In A Car Do?

How To Unstick A Thermostat In A Car? 9 Detailed Steps! (1)

In most automobiles, the thermostat’s location is inside the thermostat housing.

This is where the engine block links to the upper radiator hose. Although it is only a small part, it is very important in the engine coolant system.

The main function of the thermostat is to close the coolant flow when the system temperature is below the specified level.

Similarly, it opens the valve to let the coolant fluid go into the cooler when the operating temperature is higher than the specified level.

As a result, the engine management system can start quickly to increase the working temperature, stabilize the temperature gauge, ensure fuel economy, and avoid environmental pollution at the early stage of the engine.

What Happens When A Thermostat Sticks?

Here are some problems you might face.

A Stuck-Closed Thermostat

When the thermostat sticks in a closed position, catastrophic issues may arise. Coolant passage is disrupted, and coolant cannot reach the radiator to cool it, causing engine overheating.

In this circumstance, your engine will not receive any cooling help. The hot engine will continue to heat up, warming up the adjacent coolant and eventually overheating.

(Video) How to Test if Your Car's Thermostat is Working (Without Removing It!!)

A Stuck-Open Thermostat

Open-stuck thermostat failure means it doesn’t retain the fluid level inside long enough. Therefore, it is difficult to get your automobile warmed up.

There are limits on both the lowest and highest temperatures. Engines dislike running cold, so many leave their cars idling in the winter.

The general problem with a bad thermostat is it cannot keep the temperature gauge at a stable lever (at about 220 – 230 degrees Fahrenheit).

Do not use the vehicle when you face a car thermostat sticking. What you should do is a thermostat replacement. So for a thermostat stuck closed quick fix, what can you do?

How To Unstick A Thermostat In A Car

Can you unstick a thermostat? Yes, of course. But before getting started, it’s important to prepare necessary items to ensure your safety. Now, here’s what you’ll need:

  • Drain bucket
  • Selection of wrenches
  • Coolant
  • New thermostat

As swapping the thermostat is a straightforward procedure and doesn’t cost much money, you may wish to do this task first before resorting to more serious measures.

Just make sure your engine is absolutely cold before proceeding.

Step 1: Find your thermostat.

Usually, the thermostat is built where the top radiator hose links with the engine. Look at that place in your car. If you can’t find it, it’s highly likely that the thermostat is located in the bottom radiator pipe.

Step 2: Place a bucket under where you’re working.

Some fluid will leak, so you should have a bucket nearby to capture it and restore it to the radiator when you’re through.

Step 3: Remove the clamp.

Step 4: Pull off the hose.


Step 5: Remove the old thermostat.

Examine the new one and its gasket alongside the old set. If the new thermostat and the gasket do not agree with the used one, return to the retailer to get the correct ones.

Step 6: Lay the new gasket in place.

Remove the gasket that was surrounding the hole in which the thermostat was situated. Scrape away any stuck parts of the gasket, but take care not to accidentally cause them to drop into the hole!

Step 7: Put in and secure the new thermostat.

Remember to put the spring-side down; after that, change the bolts.

Step 8: Replace the hose and hose clamp.

Screw your hose clamp down securely but not so tightly that it cuts through the hose.

Step 9: Replace any fluid leaking from the hose.

Make cautious not to spill it on the surface where it might hurt children or animals. If you unintentionally spill fluid, remove it well before hosing down the area, and then dispose of the rag inside and seal the bag.

What Causes The Thermostat to Stick?

Low Coolant Level

The thermostat may become stuck if the coolant level drops. Coolant supports the heat removal from the car’s engine.

Thus, the engine may get sieved or overheated once there is insufficient coolant. The usage of an overheated engine may cause the thermostat to stick and other issues.

Old Or Dirty Engine Oil

Old or unclean engine oil can cause the thermostat to become stuck when closed, preventing coolant from properly circulating.


It’s advisable to keep an eye on your engine oil level then top it off as needed.

When you find the filter not working properly or there is dirt build-up on it, you can change the oil filter without changing oil, though changing both is recommended.

Coolant Needs A Replacement

A thermostat can become stuck in one position due to old coolant. This is due to the coolant’s inability to flow in a free manner.

When this occurs, the thermostat may become stuck when open. The engine will overheat as a result of this. To avoid this, it is critical to update the coolant every several years.

A Defective Thermostat

A malfunctioning thermostat can be attributed to its low quality and fault codes. You get what you pay for, so a cheap thermostat can turn out to be trash and cause problems for your driving experience.

How to Tell That the Thermostat Is Stuck

Signs Of Damage To The Thermostat Valve

Engine Overheating

Coolant will not flow into the radiator if the thermostat is closed, causing engine overheating. When cars operate in this condition for too long, there is a risk that the engine will be completely destroyed.

Unusual Temperature Changes

Users should regularly monitor the temperature gauge on the control panel. If a sharp needle falls, it may be due to a fault in the car thermostat.

Leakage Of Coolant

Another sign that the thermostat has a problem is leaking coolant. When damaged, this part will not allow liquid to flow but is trapped in the closed position.

This can cause coolant to leak through the gasket between the radiator and the reservoir, seep out of the valve housing or through the ductwork, and into the underbody of the vehicle.

How to Check A Stuck Thermostat

Before removing the thermostat from the vehicle, check the coolant temperature and flow rate.

First, you should start the car and allow the engine to idle, then open the bonnet and remove the radiator cap.

If the coolant leaks out, the thermostat is stuck. In case the water does not flow, wait until the car engine warms up to the appropriate temperature and see the results in 10-20 minutes.

But if the coolant is still not flowing and the temperature gauge rises, then the thermostat valve is having a problem.

(Video) Engine Overheating? - 9 Steps to Solve

Alternatively, to check the temperature of the coolant, the user can start with the radiator and the engine cooling.

You start the engine and use the thermometer to read the temperature in the engine block or cylinder head.

Then, proceed to check the temperature of the upper radiator pipe. If the temperature does not rise much, the thermostat valve is stuck.

In case the radiator hose remains at the same temperature but the gauge on the control panel increases suddenly, the thermostat valve is also in trouble at this time.

To check the thermostat on the outside of the car, you can put it in a pot of water on the stove, hang the thermostat half-submerged in the water tank, and do not let it fall to the bottom of the pot.

At this time, observe the temperature change on the thermometer.

If the thermostat is still closed when the water has boiled in the range of 190 – 195 degrees F, then this valve is damaged and needs to be replaced.


How To Unstick A Thermostat In A Car? 9 Detailed Steps! (2)

The thermostat, in particular, and the cooling system, in general, are the important parts of cars during operation. A stuck thermostat might cause severe issues to your vehicles.

We hope our blog has given you a clear guide on how to unstick a thermostat in a car and you can do it on your own after reading this one.

You should regularly monitor for signs of damage to the thermostat to conduct maintenance and repair when necessary. This is to ensure that the car always operates stably.

Investing in required automobile upkeep is never unnecessary. In return, you may enjoy a smoother journey without fear of unexpected mishaps.


How do you get a car thermostat unstuck? ›

To fix a thermostat that if stuck open you will:
  1. Park your car on a flat surface and allow the engine to cool.
  2. Locate the thermostat.
  3. Remove the radiator cap.
  4. Disconnect the radiator hoses from the engine.
  5. Replace the valves in the thermostat hoses.
  6. Top off antifreeze fluid levels.
Feb 21, 2022

How do I know if my thermostat is stuck? ›

If it is not flowing, wait until your engine warms up. The coolant should warm to the right temperature and begin to flow after 10 to 20 minutes. If it does not start to flow, but the temperature gauge on your dashboard rises, your thermostat is stuck closed.

What happens if a thermostat is stuck closed? ›

If the thermostat becomes stuck in the closed position, the circulation of the coolant is blocked so the coolant cannot get to the radiator to be cooled which causes the engine to overheat.

What does a stuck thermostat look like? ›

Look to see if the coolant is swirling/flowing immediately — that means the thermostat's stuck open. If the coolant doesn't flow after 10 minutes or so and continues to be stagnant after the temperature gauge indicates it's hot, the thermostat's likely stuck closed.

How do you unclog a thermostat? ›

Using a clean, soft paintbrush and a gentle touch, dust the inner workings of the thermostat. For grime or debris at points where the electronic components touch, slide an open dollar bill like dental floss between them to loosen and remove it. An alternative tool is compressed air.

Can you drive with a stuck thermostat? ›

Can I Still Drive with a Bad Thermostat? The easy answer to this question is no. While your car may be physically able to move and get you from Point A to Point B, you will want to refrain from operating your vehicle. This can lead to more parts of your vehicle being damaged, especially if the engine is overheating.

Will a stuck thermostat cause no AC? ›

Some AC problems due to a malfunctioning thermostat

When a thermostat develops repair problems, it will often lose its connection to the air conditioner. In such cases, although you will need repair technicians to fix the thermostat, you shouldn't have damage to the AC itself that will need work.

What causes a thermostat to stop working? ›

Loose connections, frayed wires, and aged wires all can cause your thermostat to eventually lose its connection to your A/C and heating system. Inspect your wiring thoroughly, making sure the connections are tight, and replace any wires as deemed necessary by you or an HVAC professional.

Will engine overheat if thermostat is stuck open? ›

If the engine is cold, it stays closed to let it warm up. As the engine heats up, the thermostat gradually opens, allowing coolant to reach the radiator. Whenever it begins to fail, the engine overheats and, if the problem is left unchecked, leads to your engine boiling over.

Will a stuck open thermostat throw a code? ›

A stuck open thermostat can cause the engine to take too long to warm up, not reach proper operating temperature at all, possibly run rich, and MAYBE set that fault code. The engine electronics are programmed to see the engine operating in a specific temperature range.

Can I fix my thermostat myself? ›

It is possible to save some money by installing or replacing your thermostat yourself, but you will need: Basic electrical knowledge. A general understanding of the type of equipment being used.

Can a stuck open thermostat be fixed? ›

Thermostats aren't really fixable. If it stops working, it's much cheaper to just replace it. That is unless the problem isn't the thermostat and it's the wiring between it and the heating unit. How can you tell if your car's thermostat is stuck open or closed?

How much does it cost to fix a stuck thermostat in a car? ›

Cost of fixing Car Thermostat

But for the average car owner, a professional mechanic will charge between $140 and $300 to replace the Thermostat in your car. The thermostat unit usually costs between $20 and $80, but a luxury or sports car can cost more. In addition, the labor will cost between $120 and $220.

Will a stuck thermostat cause no heat? ›

If a thermostat is stuck in the closed position, it will never allow coolant to circulate fully, so no heat for you. You can fix this problem by removing the lower radiator hose and installing a new thermostat.

Can a stuck open thermostat cause transmission problems? ›

if the thermostat is stuck open

you might see these issues as a result: temperature gauge reads lower than normal. heater doesn't work. automatic transmission has trouble shifting into higher gears.

How do I override my AC thermostat? ›

How do I use the override feature on my AC? Most AC units have an automatic settings panel, that is used to dictate when it will shut off or turn on. If your AC is on, you can simply press the override button to keep it on for longer, or shut off for a period of time.

How do I know if my thermostat is working? ›

Standard thermostats: Enlist a friend or family member to assist, Position one person by the thermostat and one person by the furnace. Slowly turn the thermostat from off to heat and increase the temperature. Both the thermostat and furnace should make a sound.

Should I turn off AC if it's not cooling? ›

If your ac is still not cooling there is one more thing you need to do. This is very important.... TURN IT OFF and call your HVAC service provider to assist you. We always tell our customers to turn off an ac that is not cooling properly.

How do I know if my thermostat fuse is blown? ›

A blown fuse inside your thermostat will cause the device to malfunction. You'll need to open the panel and locate the fuse. This is a small, clear cylinder with metal ends and a filament running through the center. If this filament brakes, the fuse has blown and will need replacing.

Is there a reset button on a thermostat? ›

Most heating, ventilation and cooling (HVAC) system thermostats have more than just temperature control buttons. They often have a reset button as well. Whether your HVAC system features a standard thermostat or a smart thermostat, you may discover a reset button on it.

What is a common problem with thermostat? ›

A common thermostat issue that usually results in the temperature never reaching what you have it set for. Grime can build up inside a thermostat. When this happens, the thermostat doesn't correctly gauge the temperature of the air in your house. Older thermostats can be cleaned by dusting inside the cover.

What should you never open if your car overheats? ›

In the meantime, do not attempt to open the hood; the coolant in a car that has overheated may be in excess of 230 degrees, says Reina. Once the hood is open, there's a risk of being sprayed with hot water or steam. “Your personal safety is most important,” he says.

Can a stuck thermostat cause pressure? ›

A failing thermostat would absolutely cause the system to overheat and build pressure. If you are already seeing signs of leaking near or from the thermostat housing there is a good chance this is where the problem lies.

Is it OK to drive with a thermostat stuck open? ›

Can I Still Drive with a Bad Thermostat? The easy answer to this question is no. While your car may be physically able to move and get you from Point A to Point B, you will want to refrain from operating your vehicle. This can lead to more parts of your vehicle being damaged, especially if the engine is overheating.

Can you drive with thermostat stuck closed? ›

A vehicle can run just fine if the thermostat doesn't open. It will run on the warm side, not past halfway, and heat the interior just fine. But, when the weather gets warmer outside that thermostat stuck closed will not be able to allow the reservoir water flow and the vehicle will begin to have overheating issues.


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