Parts for your 2016 Subaru Forester-Thermostat housing

2016 Subaru Forester thermostat-housing: what it does, where it sits, and how to look after it

Yes, the 2016 Subaru Forester uses a thermostat-housing. Subaru’s own technical references confirm it: the Subaru Service Manual for the Forester’s FB25 2.5‑litre and FA20F 2.0‑litre turbo engines locates the thermostat within a dedicated water inlet/outlet housing at the lower radiator hose connection on the engine. The Subaru parts catalogue lists the housing (often called the water inlet or thermostat cover) along with the thermostat and O‑ring seal for both engines. That makes the thermostat-housing a relevant, replaceable component on this model.

On the 2016 Forester, the thermostat-housing holds the thermostat in place and directs coolant flow into the engine. When the engine’s cold, the thermostat stays shut to help it warm up quickly. Once it reaches operating temperature, the thermostat opens and the housing channels coolant through the radiator to keep temps steady. A tidy seal at the housing is critical—any leak here can drop coolant levels, cause overheating, or leave tell‑tale pink or blue crust from dried coolant.

As part of routine servicing, the housing itself doesn’t have a strict replacement interval, but it should be inspected whenever coolant is changed or if there are temperature fluctuations. Subaru’s long‑life coolant typically runs for many years and high kilometres, still, it’s smart to check the housing for hairline cracks (on plastic styles), corrosion (on aluminium), and weeps around the O‑ring. If removing the housing to replace the thermostat, always fit a new genuine‑spec O‑ring and clean the mating surfaces carefully.

DIY‑ers should note the housing bolts are small and only need light torque—over‑tightening can distort the seal or crack the housing. Refill with the correct Subaru long‑life coolant mix, run the heater on hot, and bleed out air to avoid hot spots or a wandering temp gauge. If the Forester shows slow warm‑up, overheating under load, or coolant drips near the lower hose, the thermostat and housing area deserve a look.

• Common signs to watch: coolant smell under the bonnet, dried coolant staining at the lower radiator hose area, erratic temperature readings, or a low header tank.
• Best practice on replacement: new thermostat, new O‑ring, inspect housing for warping, and refresh hose clamps if they’re tired.

Where is the thermostat-housing on a 2016 Forester?
It’s mounted low on the engine where the lower radiator hose meets the block—Subaru refers to it as the water inlet or thermostat cover. On both the FB25 and FA20F, it’s secured with a couple of bolts and seals with an O‑ring. Access is easiest from underneath with the splash guard off.

What are the signs the thermostat-housing or seal is failing?
Look for dampness or dried coolant near the lower hose connection, a sweet coolant smell after parking, or slight overheating on longer climbs. A sticky thermostat can also cause slow warm‑up or temp swings. Any leak or crack at the housing should be sorted quickly to avoid overheating.

Should the housing be replaced with the thermostat?
Often the housing can be reused if it’s not cracked or warped. Always replace the O‑ring. If the housing shows damage, corrosion, or won’t seal cleanly, it’s worth fitting a new unit while you’re there—especially on higher‑kilometre Foresters where plastic can go brittle.