How to Install a Radiator Thermostat

Written by grace mclain
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The thermostat in your car is the main component that cools the antifreeze in the engine block once the engine reaches a certain temperature. The thermostat has a spring on the bottom that is regulated by the temperature of the engine block. The hotter the engine block, the higher the spring's position until it is completely upright. Once the spring is completely upright, the coolant can flow freely into the engine block.

Skill level:

Things you need

  • Fluid catch pan
  • Pliers
  • Flat head screwdriver
  • Phillips head screwdriver
  • Ratchet
  • Socket set
  • Flat metal scraper
  • Red high temperature silicone
  • Replacement thermostat

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  1. 1

    Open the bonnet of your vehicle and wait for the engine to completely cool down before removing the radiator cap from the engine.

  2. 2

    Remove the radiator cap from the radiator.

  3. 3

    Slide a fluid catch pan underneath the driver's side of the radiator. Locate the butterfly drain plug on the lower driver's side of the radiator. The butterfly plug is a screw-in plug with a small handle. Unscrew the butterfly plug with the pliers until the coolant starts to flow into the catch pan. Finish unscrewing the plug by hand. Once all of the coolant has drained out, screw the plug back in and tighten it down with the pliers.

  4. 4

    Return to the top of the engine and locate the top radiator hose. One end of the top radiator hose is connected to the top of the radiator, and the other end is attached to the thermostat housing.

  5. 5

    Loosen the clamp from around the radiator hose that is connected to the thermostat housing with the appropriate-sized screwdriver. Then, slide the clamp back onto the hose about 6 inches. Pull the hose off of the thermostat housing tube. If the hose is hard to pull off, use a flat head screwdriver to pry it off of the thermostat housing tube.

  6. 6

    Locate the two thermostat housing mounting bolts. There is one bolt on each side of the thermostat housing. Loosen and remove both of the bolts with a ratchet and socket. Pull the bolts out and set them to the side.

  7. 7

    Pull the thermostat housing off of the engine block and set it to the side. Then, pull the thermostat straight up and out of the engine block. Scrape off the old thermostat housing gasket from the bottom of the thermostat housing with a flat scraper.

  8. 8

    Lower the new thermostat into the engine block with the spring facing downward into the hole. The spring is what makes the thermostat function. Apply a thin bead of red high temperature silicone onto the bottom of the thermostat housing then press the thermostat housing gasket onto the silicone. Make sure that the holes in the gasket line up with the holes on the thermostat housing.

  9. 9

    Place the thermostat housing back over the top of the thermostat and screw the two mounting bolts back in place. Tighten the two mounting bolts with a ratchet and socket.

  10. 10

    Slide the top radiator hose onto the thermostat housing port. Then, slide the clamp over the radiator hose and the thermostat housing port. Tighten the hose onto the thermostat housing port with the appropriate-sized screwdriver.

  11. 11

    Fill the radiator up with antifreeze until the coolant level rises to the top of the radiator fill neck. Crank the engine and watch for the coolant level to drop. Keep adding antifreeze to the radiator with the engine running until the coolant stabilises at the top of the fill neck.

  12. 12

    Screw the cap back onto the radiator once the coolant level is full. Then inspect the top radiator hose and the thermostat housing for any leaks while the engine is running. Turn the engine off.

Tips and warnings

  • Red high temperature silicone is the only approved silicone for high temperature areas.
  • You can purchase this at most auto parts stores.
  • Touching a hot engine can result in serious burns. Be sure that the engine has completely cooled off for at least one to two hours before removing the radiator cap.
  • Always wear safety glasses when working inside of the engine compartment.

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