Looking for a quick fix for a thermostat stuck closed? The best solution is to replace it. You’ll need to find the thermostat housing, drain the old coolant, remove the stuck thermostat, put in a new one, and then fill your car with coolant. While there are ways to deal with a thermostat that’s stuck open, swapping it out for a new one is usually simpler and saves you trouble.

Please keep reading to learn all about fixing a thermostat stuck in your car and how to handle it smoothly.

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How do you replace a stuck thermostat in a car?

How do you replace a stuck thermostat in a car

Replacing a stuck thermostat in a car involves several steps for most vehicle makes and models. Here’s a simplified guide to help you replace a stuck thermostat:

Prepare Your Vehicle and Gather Tools

    • Ensure the engine is excellent before beginning any work to avoid burns.
    • You’ll need a few essential tools, including a wrench or socket set, screwdriver, drain pan, and possibly pliers.
    • Purchase a new thermostat and gasket (or O-ring) for your vehicle model.

Identify the Thermostat Housing

    • The thermostat is usually located at the engine end of the upper radiator hose. The housing is typically a metal or plastic case secured with bolts to the engine.

Drain the Coolant

    • Place a drain pan under the radiator drain plug (petcock) or the lowest point of the radiator hose to catch the coolant.
    • Open the petcock or remove the lower radiator hose to drain the coolant. Be sure to dispose of or recycle the old coolant properly.

Remove the Thermostat Housing

    • Carefully remove the bolts or screws securing the thermostat housing the engine. Take note of any brackets or sensors that need to be removed or disconnected.
    • Remove the housing to expose the thermostat.

Remove the Old Thermostat

    • Note the orientation of the old thermostat before removal; it’s crucial for installing the new one correctly. A valve or jiggle pin should be adequately oriented, often at the top.
    • Carefully remove the thermostat. You may need to pry it out if it’s stuck gently.

Clean the Housing Surfaces

    • Clean the mating surfaces on the thermostat housing and the engine where the gasket sits. Ensure all old gasket material and corrosion are removed for a clean seal.

Install the New Thermostat

    • Place the new thermostat into the engine block with the correct orientation, following how the old one was fitted. The spring side typically faces into the engine.
    • If your thermostat comes with a new gasket or O-ring, install it as per the manufacturer’s instructions. Some applications require a sealant.

Reassemble the Thermostat Housing

    • Reattach the thermostat housing with the new thermostat and gasket in place. Tighten the bolts to the manufacturer’s specified torque settings to avoid leaks.

Refill the Coolant System

    • Refill the radiator with coolant. If your system was completely drained, it might be an excellent opportunity to use fresh coolant mixed according to the manufacturer’s specifications.
    • Fill the coolant reservoir to the correct level.

Bleed the Cooling System

    • Start the engine and let it reach operating temperature with the radiator cap off. This process helps remove any air pockets in the system.
    • Watch the coolant level and add more as necessary. Look for steady streams of coolant without air bubbles, which indicates the system is fully bled.
    • Once done, check for leaks and ensure the heating system inside the car is working properly, indicating a correctly functioning thermostat.

Final Checks and Cleanup

    • After the engine has cooled down, recheck the coolant level and top off if necessary.
    • Dispose of the old coolant and thermostat responsibly.

Consult your vehicle’s service manual for instructions, torque specifications, and safety precautions. Different vehicles may have unique procedures for bleeding the cooling system or handling electronic sensors connected to the thermostat housing.

How to Fix a Stuck Open Thermostat

How to Fix a Stuck Open Thermostat

Suppose you find out that your car’s thermostat is stuck open while driving. In that case, you must stop immediately to prevent engine damage. Here’s a more straightforward way to handle it:

  1. Pull Over Safely: When you realize a problem, find a safe spot to pull over. Make sure the place is level, and turn off your car. This gives your engine a chance to cool off.
  2. Check the Thermostat: Once everything’s cooled down, look at the thermostat. You must remove the radiator cap first—ensure it’s not hot. Then, you’ll disconnect the hoses from the radiator to the engine. Again, check that they’re not hot to avoid burns.
  3. Replace the Thermostat: Now it’s time to swap out the old thermostat for a new one. This piece controls the temperature in your engine, so it’s essential to have one that works right.
  4. Add Antifreeze if Needed: After putting in the new thermostat, check if you need to add more antifreeze to your car. This helps keep everything running smoothly.
  5. Give it a Test: Start your car and let it run to see if the issue is fixed. If your vehicle still gets too hot, you need a new thermostat.

Following these steps will help protect your car from overheating and keep your engine in good shape. Calling a mechanic is a good idea if you’re uncomfortable doing this alone.

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How Can You Avoid a Thermostat Stuck Closed?

To avoid encountering a thermostat stuck closed, which can lead to overheating and potentially severe engine damage, it’s essential to follow a proactive maintenance schedule and heed the warning signs of a failing thermostat. Here are several strategies to prevent this issue:

Regular Maintenance Checks

  • Coolant System Inspection: Regularly inspect your coolant system, including the thermostat, radiator, hoses, and coolant fluid. Look for signs of corrosion, leaks, or wear.
  • Coolant Replacement: Follow the manufacturer’s guidelines for replacing the coolant. Old or contaminated coolant can cause the thermostat and other cooling system components to fail.

Thermostat Inspection and Replacement

  • Scheduled Replacement: Consider replacing the thermostat at regular intervals or during primary cooling system services, even if it has yet to fail. This is especially true for vehicles that have experienced overheating issues.
  • Functionality Check: Have your mechanic check the thermostat’s operation during routine maintenance. This can often be done by observing the engine’s temperature gauge for proper operation or using diagnostic tools to ensure the thermostat opens and closes at the correct temperatures.

Use Quality Coolant

  • Appropriate Coolant Type: Always use the coolant recommended by your vehicle’s manufacturer. Different engines require different coolant formulations to protect against corrosion and overheating.
  • Avoid Mixing Coolants: Different types of coolants can lead to chemical reactions that form deposits, which can clog the cooling system and cause the thermostat to stick.

Monitor Engine Temperature

  • Keep an eye on the engine temperature gauge on your dashboard. Suppose you notice the temperature rising higher than usual. In that case, it may indicate a thermostat that is beginning to stick or fail.

Listen for Overheating Signs

  • Signs that your vehicle is overheating include steam under the hood, a high reading on the temperature gauge, or a warning light on the dashboard. If you experience these signs, it’s crucial to stop driving and turn off the engine as soon as it’s safe to avoid further damage.

Check for Coolant Leaks

  • Regularly check for signs of coolant leaks under your vehicle, especially after it has been parked for a while. A low coolant level can cause the engine to overheat, leading to thermostat failure.

Educate Yourself on Your Vehicle’s Cooling System

  • Understanding how your vehicle’s cooling system works can help you identify potential issues before they become serious. Please familiarize yourself with the specific components and their maintenance schedules.

Professional Coolant System Flush

  • Consider having a professional coolant system flush performed periodically. This service can remove scale, rust, and other debris that could cause the thermostat or other cooling system components to malfunction.

By adhering to these preventive measures, you can significantly reduce the risk of experiencing a thermostat stuck closed, thus ensuring your vehicle’s engine operates within the optimal temperature range and maintains performance and efficiency.

How to Detect a Stuck Thermostat

Detecting a stuck thermostat involves observing specific symptoms and performing diagnostic tests. Symptoms can vary depending on whether the thermostat is stuck open or closed.

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Symptoms of a Stuck Open Thermostat:

  • Underheating: The engine takes longer to reach its operating temperature or may not get it, especially in cold weather.
  • Poor Cabin Heating: The heating system inside the vehicle blows cold air because the engine isn’t reaching its average operating temperature, leading to inefficient heater performance.

Symptoms of a Stuck Closed Thermostat:

  • Overheating: The most common symptom is when the engine temperature quickly rises to the red zone within minutes of starting the engine.
  • Coolant Boiling Over: Coolant may boil and overflow from the radiator or coolant reservoir due to excessive heat not being adequately regulated.

Diagnostic Tests:

  • Temperature Gauge Monitoring: Start the engine and let it idle. Observe the temperature gauge; a stuck thermostat will often cause the temperature to rise higher than usual or not rise much at all.
  • Infrared Thermometer: Use an infrared thermometer to check the temperature of the radiator hoses. If the thermostat is stuck closed, the upper radiator hose will remain calm while the engine overheats. If stuck open, the hose will warm up, but the engine temperature will remain lower than usual.
  • Coolant Flow Test: With the engine off and cool, remove the radiator cap and start the engine. If the coolant starts flowing immediately, it suggests the thermostat is stuck open, as usually, the coolant should not flow until the engine warms up and the thermostat opens.

Signs of a Bad Thermostat

Signs of a Bad Thermostat

A bad thermostat can manifest through several signs, indicating it is stuck open or closed or has erratic opening and closing cycles.

  • Engine Overheating: The most immediate sign of a bad thermostat that is stuck closed. It prevents coolant from flowing through the engine and radiator, causing the engine to overheat.
  • Fluctuating Engine Temperatures: If the thermostat opens and closes irregularly, it can cause the engine temperature to fluctuate, which is reflected on the temperature gauge or warning lights on the dashboard.
  • Cold Operation: A thermostat stuck open can prevent the engine from reaching its optimal operating temperature, leading to inefficient engine operation, increased wear, and higher fuel consumption.
  • Heater Performance Issues: Poor performance of the vehicle’s heater in cold weather can also be a sign of a thermostat that is stuck open, as the engine isn’t reaching sufficient temperature to provide hot coolant for the heating system.

Detecting a lousy thermostat early and addressing the issue can prevent more severe engine problems, including overheating, which can lead to engine failure. Regular maintenance checks and attention to the signs of thermostat failure are crucial to ensuring your vehicle’s longevity and reliable performance.

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How Do I Know if My Thermostat is Stuck Open or Closed?

Determining whether your car’s thermostat is stuck open or closed is crucial for diagnosing cooling system issues and ensuring your vehicle operates efficiently. Here’s how you can tell the difference between the two conditions:

If Your Thermostat is Stuck Open

  • Slow to Warm Up: The engine will take longer than usual to reach its optimal operating temperature. This is particularly noticeable in cold weather.
  • Poor Heater Performance: Since the engine isn’t running at its average temperature, the heating system may only blow lukewarm or even cold air, making the vehicle’s cabin uncomfortable in cold weather.
  • Decreased Fuel Efficiency: Engines run most efficiently at their designed operating temperature. A thermostat stuck open can cause the engine to run cooler than intended, which may lead to decreased fuel efficiency as the engine management system adjusts to try to warm the engine.

If Your Thermostat is Stuck Closed

  • Rapid Overheating: The most immediate and dangerous symptom of a thermostat stuck closed is the engine overheating shortly after starting. Because the coolant cannot circulate through the radiator to be cooled down, the engine’s temperature will rise quickly.
  • Boiling Coolant: You might notice steam or boiling coolant coming from under the hood, or the coolant may overflow from the reservoir due to excessive pressure and temperature.
  • Warning Lights: The vehicle’s dashboard may display warning lights indicating the engine temperature is too high.

Can a Quick Fix for a Thermostat Stuck Closed Itself?

A stuck thermostat is a mechanical issue that cannot resolve itself. The thermostat is a simple device designed to open and close at specific temperatures to regulate the engine’s cooling system. Suppose it fails to operate as planned due to mechanical failure, corrosion, or debris blocking its movement. In that case, it must be replaced to restore proper function to the cooling system.

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Can You Drive with a Bad Thermostat?

Driving with a bad thermostat is risky and not recommended for several reasons:

  • Risk of Overheating: If the thermostat is stuck closed, there’s a high risk of the engine overheating. This can cause significant engine damage, including warped cylinder heads, blown head gaskets, and, in severe cases, complete engine failure.
  • Inefficient Engine Operation: A thermostat stuck open can prevent the engine from reaching its ideal operating temperature, leading to inadequate fuel consumption and reduced engine performance.
  • Environmental Impact: Operating the engine at incorrect temperatures can also increase emissions.

If you suspect your thermostat is failing, whether stuck open or closed, it’s best to address the issue immediately. Continuing to drive under these conditions can lead to more severe and costly repairs down the line. Replacing a thermostat is generally a straightforward and cost-effective procedure that can prevent further engine problems.

 How Much Does Thermostat Replacement Cost in Cars?

The cost of replacing a thermostat in a car can vary widely depending on several factors, including the make and model of your vehicle, the price of the thermostat itself, and labour charges if you have the replacement done at a repair shop or dealership. Here’s a general breakdown:

Cost of the Thermostat

  • Economy Cars: A replacement thermostat might cost between $10 to $50 for the part alone for many economy or standard vehicles.
  • Premium or Luxury Cars: For premium or luxury vehicles or those with more complex cooling systems, the thermostat can cost between $50 and over $150 for the part.

Labor Costs

  • Labour: The labour cost can vary significantly depending on where you live and the vehicle model. Generally, labour for thermostat replacement can range from $50 to $150 or more. Some vehicles have thermostats that are easily accessible and can be replaced with minimal labour. In contrast, others may require the removal of several components, increasing the labour time and cost.
  • Total Cost: Combining parts and labour, replacing a car’s thermostat can range from as low as $60 to $200 or more for most vehicles. For luxury or high-end models, or in cases where additional parts like hoses or gaskets need to be replaced during the process, the cost can go higher, potentially up to $300 or more.

Additional Considerations

  • Coolant Replacement: If your coolant needs to be flushed and replaced during the thermostat replacement, this could add $50 to $100 to the total cost.
  • Diagnostic Fees: Some repair shops charge a diagnostic fee to determine the cause of the overheating, which can be applied to the repair cost if you choose to have the work done there.
  • Warranty and Quality of Parts: Opting for OEM (Original Equipment Manufacturer) parts over aftermarket parts might increase costs but can offer better longevity and compatibility with your vehicle.

Tips for Saving Money

  • Price Shop: It’s a good idea to get quotes from several repair shops to compare labour rates.
  • DIY: If you’re mechanically inclined, consider doing the replacement yourself. The cost would then be the price of the thermostat and any new coolant you might need.
  • Use Quality Parts: While opting for the cheapest parts can save money upfront, investing in quality parts can prevent future failures and additional repairs.

Remember, prices vary widely, so it’s always a good idea to ask for a detailed quote from your service provider before proceeding with the work. This helps avoid any surprises when it comes time to pay the bill.

FAQs on Quick Fix for a Thermostat Stuck Closed

1. Can I temporarily fix a thermostat stuck closed to drive to a repair shop?

Temporarily, you can slightly mitigate the issue by turning the heater to its highest setting. This can help draw some heat away from the engine. However, this is not a fix but a temporary measure to reduce the risk of overheating while you drive a short distance.

2. What are the risks of driving with a thermostat stuck closed?

Driving with a thermostat stuck closed can lead to engine overheating very quickly. Overheating can cause severe engine damage, including warped cylinder heads, blown head gaskets, and, in extreme cases, complete engine failure.

3. How can I tell if my thermostat is stuck closed without removing it?

Signs include the engine overheating soon after starting and the upper radiator hose remaining cool. In contrast, the engine is hot (since the coolant isn’t circulating) and possibly hears boiling or gurgling noises from the coolant system due to overheated coolant.

4. Can I unstick a closed thermostat without replacing it?

While some suggest tapping on the thermostat housing with a wrench or similar tool might temporarily unstick the valve, this is not a reliable or recommended solution. The thermostat may fail again soon after, potentially leading to engine damage.

5. How quickly should I replace a thermostat that’s stuck closed?

It should be replaced as soon as possible. It continues to drive with a stuck closed thermostat and risks severe engine damage due to overheating.

6. Can I remove the thermostat to prevent overheating until I get it replaced?

Removing the thermostat will allow coolant to flow freely, preventing immediate overheating. However, this is not advisable for regular driving because the engine needs to reach its optimal operating temperature for efficient performance. Driving without a thermostat can cause the engine to run too cool, increasing wear and potentially leading to other issues.


Regular maintenance and prompt replacement of a faulty thermostat are essential to your vehicle’s health. The steps outlined above can help you successfully replace a stuck thermostat, ensuring your car runs smoothly and efficiently. Refer to your vehicle’s service manual for specific instructions and torque specifications to avoid issues.


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