How to Replace an Engine Thermostat

An engine cooling system thermostat is used to regulate the temperature at which the engine operates and is located at the engine radiator hose inlets or outlet depending on design.

What Goes Wrong?

 Like any mechanical device, over time, a thermostat can fail, if the thermostat is stuck closed coolant can not flow into the radiator which will result in engine overheating, if the thermostat is stuck open the engine will not reach operating temperature which will cause the heater to stop working and a check engine light to come on.

What Does It Cost?

Typically replacement parts will cost between $18.00 and $40.00 on Amazon (US) and will require the cooling system to be drained and the removal of the thermostat housing. Labor time can be between .8 and 2.0 hours at a shop or dealer. If exact times or procedures are needed you can ask our experts to supply you with the information (free), or consult an online resource such as AllData DIY (pay) but this guide and video will be sufficient in most cases.

Lets Jump In!

Precautions:  Engine coolant is toxic and can be fatal to animals and children so use caution when handling. Do not open the cooling system when the engine is hot.

With the engine cold, slowly open the radiator cap to relieve pressure inside the radiator and cooling system.
open radiator cap

Remove the vehicle's under shielding to locate the radiator drain valve, loosen the valve to begin draining the coolant, close the valve once complete, if a drain plug is not found remove the lower radiator hose to drain the coolant.
drain coolant

The thermostat is located in the lower radiator inlet of the engine, loosen the hose clamp which holds the radiator hose to the thermostat housing and remove the radiator hose.
loosen hose clamp

Use a wrench or a socket to remove the housing mounting nuts or bolts.
remove housing thermostat nuts

Gently tap on the housing using a small hammer to break the seal loose and remove the housing, the thermostat will now be exposed.
remove thermostat housing

Once the housing has been removed, clean the gasket sealing surface and inspect for corrosion which will impede the new gaskets ability to seal correctly.
thermostat housing

The thermostat might be stuck in the block or intake manifold so pliers may be needed to remove, note the direction of the thermostat, the spring always goes towards the engine.
remove thermostat

Watch the Video!

Please watch this video of the job being done, then continue down the guide to glean additional helpful information.

Here is what it looks like when the thermostat is removed and the sealing gasket or O ring exposed. Clean the area using a shop towel and remove all debris which will enable the new gasket to seal completely.
remove gasket

Match the new thermostat to the old unit, designs may vary so if there is a large difference recheck the application information.
new thermostat

On this application the sealing O ring is installed onto the thermostat itself, this design will vary, but the principle is the same.
installing new thermostat gasket

On some thermostats there is an air bleed valve on the face of the thermostat body. This allows air to escape from the block when refilling the cooling system and must be located at the top of the thermostat. The plunger is the part that opens to allow the coolant to flow.
air bleed thermostat

Once the sealing surfaces are clean, install the new thermostat with the bleed hole facing upwards and the spring toward the block or intake manifold, push the thermostat into place.
reinstall new thermostat

Before reinstalling the thermostat housing, clean the sealing surface using a gasket scraper or sand paper.

Reinstall the housing onto the block or intake manifold, install mounting bolts or nuts and tighten to spec, in this case it is 12 foot pounds of torque.
reinstall thermostat housing

Reinstall the radiator hose and you are all set, refill the cooling system and start the engine, while the engine is warming up check for coolant leaks.
reinstall hose

Additional Thermostat Replacement Videos


Our certified technicians are ready to answer engine cooling system thermostat questions for free. We hope you saved money and learned from this guide. We are creating a full set of car repair guides. Please subscribe to our 2CarPros YouTube channel and check back often for new videos which are uploaded regularly.

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