Thermostat Replacement

Engine Cooling System Thermostat
How to Replace a Thermostat

Your vehicle is equipped with a thermostat. Much like the thermostat in your home, the thermostat is designed to maintain a set temperature. However, your car’s thermostat is specifically designed to maintain the engine temperature. It is part of the cooling system. Although its primary purpose is to maintain a set engine temperature, it is required for the proper operation of the vehicle’s heater and if the engine does not warm up to operating temperature or gets too hot, it will have an affect on drive ability. Certain sensors will not function properly if the engine isn’t running at a specific temperature range.

The vehicle’s thermostat is also responsible for the heater that warms your vehicle. It forces coolant to reach temperatures up to 200 degrees F. Once it is fully open and allowing coolant to freely flow through the engine and radiator, it also flows through the heater core allowing heat to enter the vehicle.

Like any mechanical device, over the years, the thermostat can become nonfunctional due to a weak spring or corrosion. If the thermostat is stuck in the closed position, coolant can not flow which will result in engine overheating, lack of heat in the passenger compartment, and drive ability problems. However, if the thermostat is stuck in the open position, chances are the engine will not reach operating temperatures in cold weather. Therefore, you may experience little to no heat in the vehicle and drivability issues.

Parts and Supplies Needed to Replace a Thermostat

1. Coolant

2. New Thermostat

3. New Hose Clamps

4. New Radiator Hose (optional)

5. Protective Clothing

6. Eye protection

7. Shop rags

Tools Needed to Complete this Job

1. Screwdriver

2. Pliers

3. Large Drain Pan to Collect Used Coolant

4. Large channel lock pliers

5. Socket set

6. Gasket scraper

Removal Instructions

Step 1. Park the vehicle on a flat surface, place the parking brake on, place the vehicle in park (A/T) or in reverse (M/T), and disconnect the negative battery terminal.

Step 2. Allow the engine to fully cool so that the radiator is cool to the touch.

Step 3. Locate the radiator drain plug on the lower section of the radiator. It will look like a wing nut. Place the large drain pan under it and drain approximately half of the coolant from the radiator.

Step 4. Place the coolant in a safe place to be reused. NOTE: Animals are attracted to coolant. It can be fatal if they drink it, so make sure to keep it out of their reach.

Step 5. Locate the thermostat housing. If you can’t find it, follow the upper radiator hose to the engine. It should end at the thermostat housing.

Step 6. Loosen the clamp that attach the radiator hose to the housing. Some clamps will require a screwdriver others will require pliers to release pressure . NOTE: Some coolant will still be in the hose.

Step 7. Once you remove the hose clamps, twist the rubber radiator hose where it attaches. Large pliers usually make this job easier. While twisting, pull the hose from the housing..

Step 8. Once the radiator hose is removed, inspect it for dry rot, wear, and damage

Step 9. OPTIONAL This is the perfect time to replace old or damaged radiator hoses. If it appears to be original, is in poor condition, or is leaking, disconnect the hose from the radiator and replace it.

Step 10. The thermostat housing is bolted in place. Carefully remove the housing to expose the thermostat. NOTE: From heat and the years, the housing may be stuck in place and require you to pry it away from the engine. Be careful when doing this. Most housings are made from aluminum and can break.

Step 11. Remove the old thermostat. NOTE: Take note as to how the thermostat is positioned so that you can reinstall the new one facing the same direction.

Step 12. With the gasket scraper, clean all old gasket material from both the engine and the housing, being careful not to damage them.

Step 13. Once all of the old gasket material is removed, clean and dry the area with a shop towel or rag. Both surfaces need to be clean and dry before replacement.

Installation Instructions

Step 1. Install the new thermostat facing the same direction as the old one. NOTE: Make sure the thermostat is centered and if there is a recess, it sits firmly in it.

Step 2. Place the new gasket or o-ring in position and install the thermostat housing. Tighten the bolts equally. Snug them first before the final torque for your vehicle is reached.

Step 3. Reinstall the radiator hose, tighten the new clamps, and refill the radiator and overflow.

Step 4. At this point, reconnect the negative battery terminal, and start the engine and turn the heater on high so air can escape from the system.

Step 5. Replace the radiator cap once you are confident the coolant level is full, allow the engine to reach operating temperature, and check for leaks.

Best Practices

  • This is a good time to replace radiator hoses and clamps. 
  • This is a good time to flush the cooling system. 
  • Never work on a the cooling system when it is hot.

If further assistance is needed, our certified car repair technicians are ready to answer your car questions. Also, gain manufacturer specific instructions and information by clicking - Auto Repair Manual

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Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-08-16)