Parts for your 2017 Subaru Forester-Thermostat housing

2017 Subaru Forester thermostat housing — what it is and how to look after it

Yes, the 2017 Subaru Forester uses a thermostat housing. Technical sources that confirm this include the Subaru Service Manual (2017MY Forester, Cooling System – Thermostat) and the Subaru parts catalogue (Group 21 – Cooling), which both show a thermostat and cover/housing mounted at the lower radiator hose outlet on FB25 2.5i models and FA20F 2.0 XT models. The housing bolts to the water pump area and seals with an O-ring.

The thermostat housing’s job is to hold the thermostat in the right spot, seal the coolant path, and channel coolant either through the radiator or the bypass depending on temperature. It helps the engine warm up smartly, then keeps it right in the sweet spot once up to temp. When it’s doing its thing, drivers get consistent cabin heat, stable temp gauge readings, and the engine runs efficiently. If it’s not happy, there can be coolant leaks, slow warm-up, or overheating.

• Tell-tales of trouble: pink/green residue or dampness around the housing
• Temperature swings or an overheating warning under load
• Heater blowing cool air after a drive
• Sweet coolant odour and a drop in the coolant level

As part of routine servicing, it’s smart to inspect the housing, O-ring, and hose connections any time coolant is changed or the front of the engine is accessed. Many technicians replace the thermostat and O-ring preventatively during a major cooling-system service or around high mileage/kilometres, especially if there’s any sign of sticking or leakage. Always refill with Subaru-approved long-life coolant at the correct mix, and bleed air properly so the Forester doesn’t end up with hot spots.

• Clean the mating surfaces and fit a fresh O-ring, don’t use sealant unless the factory procedure calls for it
• Torque the housing bolts to factory spec and use quality hose clamps
• Run the heater on full hot during bleeding, top up the header tank, and recheck cold the next day
• If the old housing is warped or cracked, replace it rather than reusing
• On turbo XT models, access is tighter, allow more time and follow the service manual steps

Looked after properly, the Forester’s thermostat housing is a fit-and-forget bit of kit that helps the boxer engine stay reliable across Aussie and Kiwi conditions.

Where is the thermostat housing on a 2017 Subaru Forester?

It sits low at the front of the engine, where the lower radiator hose meets the engine. On the FB25 2.5i and FA20F 2.0 XT, it’s bolted to the water pump area and sealed with an O-ring. You’ll spot it by tracing the lower hose from the radiator to the engine.

Is the housing different between the 2.5i and 2.0 XT?

The location and function are similar, but the casting/cover and associated plumbing can differ between the naturally aspirated and turbo engines. Always match parts to the VIN or engine code to avoid fitment headaches.

Should the housing be replaced when changing the thermostat?

Not always. If the housing is clean, flat, and uncracked, a fresh thermostat and O-ring usually suffice. Replace the housing if there’s warping, corrosion, stripped threads, or persistent leaks after correct installation and torque.