Parts for your 2015 Subaru Forester-Thermostat housing

2015 Subaru Forester thermostat housing: what it is and how to look after it

Yes — a thermostat housing is fitted to the 2015 Subaru Forester. Subaru’s Factory Service Manual (2015MY Forester, Cooling section) and the Subaru parts catalogue both show a “water inlet” (thermostat housing) that clamps over the thermostat at the lower radiator hose/water pump inlet on both the 2.5i (FB25) and 2.0XT (FA20F) engines. It’s a serviceable part with a replaceable O‑ring/gasket.

The thermostat housing on a 2015 Forester isn’t just a cover, it’s the pathway that guides coolant into the water pump while securely locating the thermostat and sealing the joint. By keeping the thermostat seated and leak-free, it helps the engine warm up quickly, stay at a steady operating temperature, and shed heat under load. Subaru labels the housing “water inlet,” and depending on engine and market it’s typically cast aluminium or a high-grade composite, sealed with a dedicated O‑ring rather than sealant.

For servicing, think of the housing as a guardian for the thermostat and a common spot to check when chasing coolant leaks. Typical signs it needs attention include dampness or crusty residue around the lower radiator hose area, slow warm‑up, fluctuating temperature gauge, or overheating. If the housing’s mating face is clean and flat and there are no cracks, a fresh O‑ring and new hose clamp often sort minor weeps. If it’s pitted, warped or cracked, replace the housing.

When replacing the thermostat or housing on a Forester:

• Drain the coolant safely and pull the undertray for access.
• Remove the lower radiator hose and the housing (“water inlet”).
• Clean the mating surfaces, do not gouge the aluminium.
• Fit a new genuine thermostat and O‑ring, orienting the bleed feature as per the FSM, then tighten the housing bolts to the factory spec.
• Refill with Subaru Super Coolant (blue, long‑life) at the correct mix, bleed air with the heater on, and check for leaks.

This isn’t a scheduled “every X kilometres” replacement on most cars in Australia and New Zealand, but it’s smart to inspect the area at each major service and consider replacement of the thermostat, O‑ring and possibly the housing around high mileage, after an overheating event, or if towing/heat load is frequent. Stick with genuine or high‑quality aftermarket parts, refresh ageing spring clamps, and avoid RTV on O‑ring joints — Subaru’s FSM explicitly calls for an O‑ring seal only.

Technical sources referenced: Subaru Factory Service Manual (2015MY Forester, Cooling section) and Subaru parts catalogue listings for the FB25/FA20F water inlet (thermostat housing), thermostat and O‑ring.

Popular questions about 2015 Subaru Forester thermostat housing

Where is the thermostat housing on a 2015 Subaru Forester?
It sits low at the front of the engine, where the lower radiator hose meets the water pump inlet. On most cars it’s easiest to see and reach from underneath with the undertray removed. Subaru labels this piece the “water inlet.”

Do I replace the whole housing or just the O‑ring/thermostat?
Often, a new thermostat and O‑ring fix temperature or minor leak issues. Replace the housing if you spot cracks, corrosion pitting, or a warped flange that won’t seal. If the hose clamp is tired, swap that too — it’s a cheap win against future weeps.

What coolant should be used after thermostat housing work?
Use Subaru Super Coolant (blue) or an approved equivalent that meets Subaru’s spec, mixed correctly with demineralised water if not pre‑mixed. After refilling, bleed air thoroughly with the heater on and recheck the level after a short drive once the engine cools.