How to Unstick a Thermostat in a Car: A Comprehensive Guide

Have you ever experienced your car overheating? One of the reasons why this could happen is a stuck thermostat. A thermostat is a vital component of your car’s cooling system that regulates the engine’s temperature. When it gets stuck, it can cause your engine to overheat, leading to significant damage. In this guide, we’ll show you how to unstick a thermostat in a car.

What is a Thermostat?

A thermostat is a mechanical valve that regulates the flow of coolant in your car engine. It typically has a spring, a temperature-sensitive element, and a valve. When the engine is cold, the spring keeps the valve closed, preventing the coolant from flowing into the radiator. As the engine warms up, the temperature-sensitive element expands, compressing the spring and opening the valve to allow coolant to flow into the radiator, thus maintaining the engine’s operating temperature.

What Causes a Thermostat to Stick?

A thermostat can get stuck for several reasons, including:

  • Corrosion: Over time, the thermostat’s components may corrode, causing it to stick.
  • Dirt and debris: Dirt and debris can accumulate around the thermostat, preventing it from opening or closing properly.
  • Age: With age, the thermostat’s components may wear out, causing it to stick.
  • Manufacturing defect: In some cases, the thermostat may have a manufacturing defect, causing it to stick.

Signs of a Stuck Thermostat

Here are some signs that your car’s thermostat may be stuck:

  • Your car’s temperature gauge shows that the engine is overheating.
  • Your car’s heater is not working correctly.
  • Your car’s engine takes longer than usual to warm up.
  • Your car’s engine coolant is leaking or discolored.
  • Your car’s radiator hoses are soft or collapsing.

How to Unstick a Thermostat in a Car

Here are some steps on how to unstick a thermostat in a car:

Step 1: Turn off the engine and let it cool down

Before you start working on your car’s cooling system, make sure to turn off the engine and let it cool down. This is to prevent any burns or injuries from hot engine components.

Step 2: Locate the thermostat

The thermostat is usually located in the upper radiator hose, where it connects to the engine. Consult your car’s owner’s manual to locate it.

Step 3: Remove the thermostat housing

Remove the thermostat housing bolts and carefully pry off the housing cover. Be careful not to damage the gasket or housing.

Step 4: Inspect the thermostat

Inspect the thermostat for any signs of damage, corrosion, or debris. If it looks stuck, try to gently pry it loose with a screwdriver. Be careful not to damage the thermostat or housing.

Step 5: Clean the thermostat and housing

Clean the thermostat and housing with a soft-bristled brush and a degreaser or soapy water. Be sure to remove any dirt, debris, or corrosion.

Step 6: Test the thermostat

Test the thermostat by placing it in a pot of boiling water. It should open when the water reaches the appropriate temperature, and close when it cools down. If it doesn’t, replace it with a new one.

Step 7: Reinstall the thermostat housing

Reinstall the thermostat housing cover and gasket, and tighten the bolts to the manufacturer’s specifications. Be careful not to overtighten them, as this can damage the housing or gasket.

Step 8: Refill the cooling system

Refill the cooling system with a 50/50 mix of coolant and distilled water. Be sure to bleed any air pockets from the system.


A stuck thermostat can cause significant damage to your car’s engine if left unchecked. If you notice any signs of a stuck thermostat, such as overheating or poor heater performance, it’s essential to take action immediately. By following these steps on how to unstick a thermostat in a car, you can ensure your car’s cooling system is working correctly and prevent any future issues.