How to fix a change car thermostat?

What is the Car Thermostat all about?

The car thermostat plays an important role from the moment you first start your vehicle. Its main purpose is to monitor engine coolant temperature to properly regulate the coolant flow through the radiator ensuring the engine is operating at the right temperature. When the engine is cold, the thermostat will block coolant flow from going into your engine allowing the car to warm up as quickly as possible. As the temperature rises, the thermostat will slowly open. By the time the engine reaches normal operating temperature, the thermostat will be fully opened, allowing coolant to flow through the engine. The hot coolant from the engine will flow into the radiator where it will then cool down, the water pump pushes the lower temperature coolant from the radiator into the engine and the cycle continues.

Keep in mind

  • Timing is everything for a thermostat - it opens and closes at just the right moment to keep the engine running at the optimum temperature.
  • If the thermostat won’t open, then coolant can't circulate from the radiator throughout the engine.
  • A stuck closed thermostat can cause very high engine temperatures and damage to vital engine components may occur.
  • On the other hand, if the thermostat can’t close, or is stuck open, engine temperature will remain low and not reach normal operating temperature, which may cause reduced fuel economy, excessive deposits to build up in the engine, and prevent heat from entering the interior through the heater vents.

How it's done

  • Remove the used thermostat by putting a drain pan under the radiator’s drain plug to catch engine coolant.
  • Loosen the drain plug with the proper removal tool, pliers, wrench, socket and ratchet to drain the coolant into the drain pan.
  • Locating the thermostat, remove necessary hoses and fittings attached to the thermostat housing and remove the mounting bolts to the thermostat housing.
  • Access the thermostat, remove and replace the thermostat.
  • Prep the mating surface of the thermostat housing and the engine by using a gasket scraper to clean off any excess sealing material and use the provided gasket.
  • Torque the mounting bolts of the thermostat housing to factory specifications.
  • Reinstall necessary hoses and fittings.
  • Carefully tighten the radiator drain plug, be careful not to over-tighten.
  • Replace the used coolant with new coolant, refilling the coolant reservoir or radiator
  • Turning the vehicle on and checking for any leaks making sure all air has escaped out of the cooling system.
  • Dispose the coolant in compliance with environmental standards in your state.

How can you tell you've fixed it correctly?

You’ll know you’ve done the job correctly if your heater is working, hot air is blowing out of your vents, and when the engine reaches operating temperature yet doesn’t overheat Make sure there isn’t any coolant leaking from the engine while the vehicle is running. The check engine to make sure that light remains off.


  • The check engine light may be on.
  • High-temperature reading
  • Low-temperature reading
  • No heat blowing out of the vents
  • Temperature changing erratically

How important is this service?

The thermostat prevents your engine from overheating. If not cared for as soon as possible, it can affect the fuel economy, emissions, engine performance, and longevity of the life of your car’s engine.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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