Parts for your 2013 Subaru Impreza-Thermostat housing

2013 Subaru Impreza Thermostat Housing — What It Does, Where It Lives, and How to Look After It

Technical sources confirm the 2013 Subaru Impreza (FB20 2.0‑litre) uses a thermostat housing. The Subaru Service Manual for the FB20 cooling system specifies the thermostat installed in the “water inlet” on the front of the engine, and the Subaru Genuine Parts catalogue lists a separate water inlet/thermostat housing and O‑ring for this model. Aftermarket catalogues for the 2012–2016 Impreza also supply direct‑fit thermostat housings and gaskets, reinforcing that this part is present and serviceable.

The thermostat housing on a 2013 Impreza holds the thermostat in place and directs coolant flow from the lower radiator hose into the engine. By keeping the thermostat sealed and correctly positioned, it helps the engine warm up briskly, then maintains a steady operating temperature for good fuel economy, heater performance, and long engine life. On the FB20 it’s mounted low at the front of the engine, bolted to the water pump area, and sealed with an O‑ring. Many are composite/plastic, some replacements are aluminium.

While the housing itself isn’t a frequent flyer for failures, age, heat cycles and coolant neglect can harden the O‑ring or warp plastic flanges. That’s when slow seeps, crusty coolant traces, or a sweet smell under the bonnet show up. A sticky thermostat can also mimic housing issues with overheating, slow warm‑up, or temp gauge swings.

As part of routine servicing, it’s smart to:

• Inspect the housing area every service for dampness, white/green crust, or pink staining.
• Check the lower radiator hose clamp and hose condition while you’re there.
• Use the correct Subaru Super Coolant (blue) or an approved equivalent, keep a 50/50 mix with demineralised water if using concentrate.

Replacement is straightforward with basic sockets and a drain pan. Allow the engine to cool completely, drain enough coolant to sit below the housing, remove the lower hose and housing bolts, swap the thermostat and O‑ring, then refit. Avoid sealant unless the manual specifically calls for it—Subaru uses an O‑ring seal here. Clean the mating faces, snug the bolts to spec (don’t overtighten plastic), refill with the correct coolant, and bleed air: cabin heater on HOT, nose slightly uphill if possible, and use a spill‑free funnel to burp the system. Watch for stable temperature and hot cabin air on the test run.

There’s no hard‑and‑fast replacement interval for the housing itself. Many owners replace the thermostat and O‑ring proactively around 160,000–200,000 km, or whenever the water pump, radiator, or hoses are being done. If there’s any leakage, warping, or cracking, a new housing is cheap insurance against bigger dramas.

FAQs

Where is the thermostat housing on a 2013 Subaru Impreza?
It’s at the front lower side of the engine, under the bonnet near the lower radiator hose connection. On the FB20 engine it’s part of the water inlet on the water pump side, secured with a couple of bolts and sealed by an O‑ring.

What coolant and how much does it need after replacing the housing?
Use Subaru Super Coolant (blue) or an approved equivalent meeting Subaru specs, mixed 50/50 if using concentrate. System capacity is roughly 6–7 litres, a typical housing/thermostat job won’t drain it completely, but have enough on hand to top up and properly bleed the system.

Do you need sealant on the thermostat housing?
No sealant is usually required. The FB20 housing uses a dedicated O‑ring. Fit a fresh O‑ring, lightly lubricate it with coolant, and ensure the surfaces are clean. If the service manual for your exact engine code specifies otherwise, follow that guidance, but RTV on the O‑ring face is generally a no‑go.