Parts for your 2017 Subaru Forester-Thermostat

2017 Subaru Forester thermostat — what it does and when to replace it

A thermostat is absolutely fitted to the 2017 Subaru Forester. For both the 2.5‑litre FB25 and 2.0‑litre FA20 engines, Subaru’s service manual and the Subaru Technical Information System describe a wax‑pellet thermostat mounted in the water inlet at the lower radiator hose on the front of the engine. Major OE and aftermarket catalogues (e.g., Subaru genuine parts, Tridon, Gates) list a thermostat for this model with an opening temperature around the low‑80s °C and full opening in the mid‑90s °C range. So yes—this Forester uses a conventional, serviceable thermostat as part of its cooling system.

The thermostat’s job is to help the Forester warm up quickly, then hold the engine at a steady operating temperature for performance, efficiency, emissions control and reliable cabin heat. By staying shut when cold, it speeds warm‑up. As coolant temp rises, it opens and lets more flow to the radiator, keeping things in the sweet spot.

While the thermostat isn’t usually a scheduled replacement item, it’s smart to treat it as part of cooling‑system servicing. Subaru’s long‑life coolant change intervals vary by market and build year, so owners should follow the maintenance schedule in the handbook and inspect the thermostat whenever coolant is replaced. Many workshops also renew the thermostat proactively when the water pump or related cooling components are off the car, or after any overheating event.

Handy service pointers for a 2017 Forester thermostat:

• Use a quality OE‑spec thermostat and a new O‑ring/seal.
• Fit it with the jiggle pin/air bleed at the 12 o’clock position (per Subaru workshop practice).
• Refill with the correct Subaru‑spec coolant mix, bleed thoroughly, run the heater on HOT, and recheck the level after a proper road test and cool‑down.
• Dispose of old coolant responsibly—pets and wildlife are attracted to it.

Common signs the thermostat needs attention include:

• Overheating under load or at idle, or the fans running more than usual.
• Slow warm‑up, lukewarm heater, and a Check Engine Light with code P0128 (coolant temperature below thermostat regulating temperature).
• Temperature gauge wandering up and down, or big temperature differences between the upper and lower radiator hoses.

If any of that shows up, testing or replacement is low‑cost insurance. Fitted correctly with fresh coolant, a new thermostat restores stable temps and helps the Forester feel spot‑on again under Aussie and Kiwi conditions.

Popular questions

Where is the thermostat on a 2017 Subaru Forester?
It sits in the water inlet housing at the end of the lower radiator hose on the front of the engine. Removing that housing reveals the thermostat and its O‑ring. Access is straightforward with the car cool and the coolant drained.

What temperature does it open at?
Most OE‑spec units for the 2017 Forester begin to open in the low‑80s °C and are fully open in the mid‑90s °C. Exact figures can vary by supplier and market, stick with an OE‑equivalent for correct warm‑up and cooling performance.

Should it be replaced as preventive maintenance?
It’s not typically on a fixed interval, but many technicians replace it during major cooling‑system work, after an overheating incident, or at higher kilometres if it’s original. Any symptoms like P0128, overheating, or slow cabin heat are a cue to test or swap it.