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How to Change the Thermostat in a Subaru Forester

by Dan Ferrell

The thermostat on your Subaru Forester helps control engine temperature by allowing coolant to circulate when the engine is hot, and reducing coolant circulation when the engine is cold. This keeps the engine operating within a predetermined temperature range. However, the thermostat unit may fail after years of service, allowing the engine to over heat or keeping it under operating temperature. When this happens, you can replace the thermostat with a few tools you might already have in your toolbox and following these steps.

Removing the Thermostat

Open the hood and place a drain pan under the radiator drain valve.

Remove the radiator cap.

Open the radiator valve and let the coolant from the radiator drain.

Close the radiator valve once the coolant has finished draining.

Raise the front of the vehicle using a floor jack and safely support it on two jack stands.

Remove the engine under cover using a wrench or ratchet and socket.

Disconnect the lower radiator hose from the thermostat housing on the engine side using a pair of rib joint pliers, Phillips screwdriver or ratchet and socket, depending on type of clamp used on your particular model.

Unscrew the two thermostat housing mounting bolts using a ratchet and socket.

Remove the thermostat housing and thermostat unit from the vehicle.

Installing the Thermostat

Clean the thermostat housing and engine mating surfaces using a soft brush to avoid damaging the surfaces.

Set the new thermostat in place along with a new rubber ring. Make sure the thermostat spring points towards the engine and the jiggle pin faces upward.

Install the thermostat housing and start the two mounting bolts by hand to avoid damage to the threads.

Tighten the bolts using a ratchet and socket.

Install the lower radiator hose on the thermostat housing and tighten the clamp using a pair of rib joint pliers, Phillips screwdriver or ratchet and socket, depending on type of clamp used on your particular model.

Replace the engine under cover using a ratchet and socket.

Lower the vehicle.

Refill the cooling system with 50 percent water and 50 percent new anti-freeze. Pour the coolant through the radiator neck using a funnel if necessary.

Replace the radiator cap.

Refill the coolant reservoir with coolant, bringing the level between the Low and Full marks.

Start the engine and let it idle for about three minutes to bring the engine to operating temperature.

Check the coolant reservoir level and add if necessary to bring the level between the Low and Full marks.

Turn off the engine.


  • Always store coolant in a closed container and dispose of it properly. The sweet taste of ethylene glycol in antifreeze may attract cats, dogs and even young kids with fatal results. Removing the radiator or coolant reservoir cap in a hot engine may blow coolant out and cause severe burns or injuries. Makes sure the coolant is under low temperature before removing the radiator or reservoir tank cap.

Items you will need

About the Author

Since 2003 Dan Ferrell has contributed general and consumer-oriented news to television and the Web. His work has appeared in Texas, New Mexico and Miami and on various websites. Ferrell is a certified automation and control technician from the Advanced Technology Center in El Paso, Texas.

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Photo Credits

  • Photo courtesy of IFCAR at