How to fix a stuck thermostat in a car?

Author: Dr. Ruth Boyle Sr.  |  Last update: Friday, May 22, 2026

You can try to clean or knock on a thermostat to get it unstuck. However, that's only a short-term fix you should not rely on. Remember: a stuck thermostat is terrible news for your engine, regardless of whether it's stuck open or closed. So, the best thing you can do is replace your stuck thermostat with a new one.

How do you free up a stuck thermostat?

Yes, you can fix a stuck closed thermostat by first allowing the engine to cool, then locating the thermostat and carefully removing it from the housing, and finally replacing it with a new thermostat and gasket before reassembling the housing.

Is it OK to drive car with a stuck thermostat?

Yes, you can drive a car with a thermostat stuck open, but it's not ideal and could lead to several problems over time.

What are the symptoms of a sticking thermostat?

If a car thermostat is stuck open, symptoms may include the engine taking longer to warm up, the temperature gauge reading lower than usual, poor fuel economy, and the engine running cold. In some cases, the heater may not produce warm air.

How to fix a bad thermostat in a car?

1. Clean the housing and the engine surface where the thermostat sits. You want a smooth surface to seal against leaks. 2. Install the new thermostat and gasket, double-checking the orientation. 3. Re-fill the coolant and bleed any air from the system. Trapped air can give you false readings.

How to Tell Car Thermostat Is Bad (Symptoms of Stuck Open Stuck Closed and Overheating)

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

Car thermostat replacement time is 30 to 60 minutes, depending on the make of the car. It will cost you around $190 to $350, including labor. Thermostat repairs usually take more time, requiring extra time to diagnose and analyze the vehicle's thermostat. It can take up to 2 hours.

How do you fix a malfunctioning thermostat?

How to Troubleshoot and Fix a Broken Thermostat
  1. Step 1: Verify Temperature Settings. ...
  2. Step 2: Inspect the Power Supply. ...
  3. Step 3: Reset the System. ...
  4. Step 4: Clean the Thermostat. ...
  5. Step 5: Calibrate the Thermostat. ...
  6. Step 6: Test the HVAC System. ...
  7. Step 7: Upgrade to a Smart Thermostat.

How can I test if my thermostat is bad?

When you set the thermostat above or below the current room temperature, you should hear a click, and the AC or furnace should kick on almost immediately. If you make changes at the thermostat and nothing happens, that's the first sign you have a bad thermostat.

What are the symptoms of a bad head gasket?

Common Signs of a Bad Head Gasket
  • Coolant Loss: Keep an eye on your coolant levels — a significant drop is a red flag. ...
  • White Smoke from the Tailpipe: Some white smoke from the exhaust pipe of a cold engine is normal. ...
  • Engine Knocking: Blown head gaskets can lead to poor compression. ...
  • Milky Oil: Check your engine's oil.

How much does it cost to replace a thermostat?

The average cost of a new thermostat, including installation, ranges in price from $50 to $500 or more based on several factors including the type of thermostat, labor costs, the complexity of the installation, and more.

Will a stuck thermostat throw a code?

A stuck thermostat will also trigger several indicators, warnings, and fault codes. As you read above, you'll first notice the blue low-temperature indicator that constantly stays on.

What causes a thermostat to stick?

Due to corrosion or aging, your car's thermostat can get stuck in a closed position. If this happens, the thermostat will not let the coolant reach the radiator, and, as mentioned above, the engine will overheat, causing severe damage. One of the lesser-known issues is the polar opposite of overheating.

Will a stuck thermostat cause no AC?

So, can a bad thermostat cause your AC not to cool? Absolutely.

How to check if coolant is flowing?

Well check the resivor with the car running if there is a change in fill level when you remove the cap then it is flowing, or keep an eye on the temp dials once the temp starts rising feel the tube that goes from the top of the radiator to the engine, if it feels warm then the coolant is flowing.

What can be mistaken for a blown head gasket?

A lot of the problem is due to the similarity between issues with head gaskets and other engine components, such as the following: A chipped or warped cylinder head, which could affect the head gasket, but wouldn't necessarily be the result of a blown head gasket.

What are the signs of a cracked engine block?

How to Tell if I Have a Cracked Engine Block?
  • Poor engine performance caused by low engine compression;
  • Visible engine smoke;
  • Engine overheating caused by leaking antifreeze;
  • Discoloration in a car's oil or antifreeze;
  • Leaking oil or coolant;
  • Frozen coolant in the radiator;
  • Excessive smoke from the exhaust; and.

What are the symptoms of a bad water pump?

6 signs your water pump is failing ​
  • Coolant Leak. The water pump has several gaskets that can be damaged or worn out over time. ...
  • Engine Overheating. ...
  • High Pitched, Harmonic Whining Noises. ...
  • Water Pump Rust and Corrosion. ...
  • Steam comes out from under your hood. ...
  • Holes or leakage system on the dry side of the water pump.

How to reset a thermostat?

Most modern thermostats will have a clearly marked reset button inside the panel. It's usually small and recessed, so you might need a pointed object like a paperclip to press it. For those wondering specifically how to reset air conditioner thermostat models, the process is generally the same.

How do you know if your car needs a new thermostat?

Here are four signs that it may need to be replaced.
  1. High Temperature. One of the first signs that your thermostat may need replacement is how high the temperature inside gets. ...
  2. Cold Engine. ...
  3. Temperature Gauge Issues. ...
  4. Coolant Level Issues.

What happens when a car thermostat goes bad?

A properly functioning thermostat regulates coolant flow to the heater core, allowing it to provide warm air to the cabin. Low Coolant Levels: A failing thermostat can cause coolant to get trapped in the engine, leading to low coolant levels in the radiator.

Why is my thermostat stuck on one temperature?

If this doesn't work, try resetting your thermostat with the reset button, changing the batteries, or cleaning off any dust and dirt inside. If the temperature is still stuck, an electrical or display issue might be to blame. Contact an HVAC professional for further help.

Will a bad thermostat run a code?

While there is a small chance that there is an issue with the running temperature of your engine, by far the most common issue with trouble code P0128 is a faulty thermostat. The exact location of the thermostat and issues related to a damaged thermostat may vary depending on your vehicle.

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