Parts for your 2016 Subaru Forester-Thermostat

2016 Subaru Forester thermostat — what it does and how to look after it

Yes, the 2016 Subaru Forester uses a conventional engine coolant thermostat. Technical references that confirm this include the Subaru Forester SJ (2014–2018) Factory Service Manual, Engine Cooling System section, the Subaru Genuine Parts catalogue for FB25 (2.5-litre) and FA20F (2.0-litre turbo) engines, which lists a thermostat assembly and gasket, and workshop databases such as Haynes and ALLDATA that detail removal, testing and refit procedures. It’s a wax‑pellet type unit fitted in the water inlet housing at the front of the engine, in the lower radiator hose area.

The thermostat’s job is simple but critical: it helps the Forester warm up quickly and then holds the engine at the correct operating temperature for efficiency, performance and emissions. When cold, it stays shut so coolant recirculates inside the block and heads, getting up to temp smartly. Once it reaches the factory‑specified temperature range, it opens and lets coolant flow through the radiator. That steady temperature also keeps the cabin heater happy and the engine oil at the right viscosity.

As part of regular servicing, it’s smart to give the thermostat and housing a once‑over whenever coolant is changed. Look for dried coolant stains, crusty deposits, or a perished O‑ring. Common clues a thermostat’s on the way out include:

• Slow warm‑up, or the temp gauge sitting low while driving (stuck open)
• Overheating or sudden temp spikes (stuck closed or sticking)
• Heater going cold at speed, then hot at idle
• Check Engine Light with a P0128 coolant temperature code

Replacement isn’t typically a scheduled item, but many techs will renew it proactively during a major cooling‑system overhaul or water pump job, or by high kilometres/years. On this Forester, stick with a genuine‑spec thermostat and the correct Subaru O‑ring, using the wrong temperature rating can cause drivability issues and fault codes.

When fitting: let the engine cool completely, drain enough coolant, remove the housing, note the thermostat’s orientation (including the air‑bleed jiggle pin), install the new unit and seal, and torque the housing bolts to spec per the service manual. Refill with Subaru‑approved premix coolant, bleed the system with the heater on full hot, squeeze the upper hose to purge air, top up the reservoir, and check for leaks. Dispose of old coolant responsibly. A clean radiator cap and fresh coolant go a long way to keeping the Forester happy under the bonnet.

Where is the thermostat on a 2016 Forester?

It’s mounted in the water inlet housing on the front of the engine, in the lower radiator hose path. On FB25 and FA20F engines it’s accessed from the front—remove the lower hose and housing for removal.

What are the signs the thermostat needs replacing?

Slow warm‑up, temperature fluctuations, overheating, poor cabin heat at speed, and a P0128 code are the big giveaways. Any coolant seepage around the housing or a flattened O‑ring also points to replacement time.

Do they need a special bleed after replacement?

Yes—use the correct Subaru coolant, run the heater on full hot, elevate the fill point if possible, and massage the hoses to purge air. Top up the reservoir after a few heat cycles as trapped air works its way out.