Parts for your 2010 Subaru Impreza-Thermostat housing

2010 Subaru Impreza Thermostat Housing

Based on Subaru’s 2010 Impreza Factory Service Manual (Cooling System section) and OEM parts catalogues, the 2010 Subaru Impreza does use a thermostat housing. On EJ-series engines fitted to this model year (including 2.0 and 2.5 variants, naturally aspirated and turbo), the thermostat sits in a bolt-on housing at the water pump outlet, where the lower radiator hose connects. So the thermostat housing is absolutely relevant and serviceable on this vehicle.

The thermostat housing’s job is to secure the thermostat, seal the coolant path, and provide the outlet neck for the lower radiator hose. As the engine warms, the thermostat opens to regulate coolant flow through the radiator, keeping temperatures in the sweet spot for performance and longevity. A healthy housing ensures the thermostat seals correctly, prevents leaks, and keeps the cooling system pressurised.

On a 2010 Impreza, the housing is mounted low at the front of the engine, near the water pump. It’s usually cast alloy on EJ engines, and it uses an O-ring or gasket to seal against the pump body. Over time, housings can corrode, the sealing face can pit, or the hose neck can crack—especially if coolant hasn’t been changed on schedule or if mixed coolants were used.

• Common clues it’s time to inspect or replace: coolant weep around the lower hose neck, crusty white/green deposits, overheating at speed, slow warm-up, or repeat air in the system after bleeding.

During routine servicing, it’s smart to inspect the housing whenever coolant is changed (typically every few years or as per Subaru’s schedule for its Long-Life/Super Coolant). Look for staining, pitting, or deformation, and always check the condition of the O-ring. If the thermostat is being replaced, fit a quality OEM-spec thermostat, renew the O-ring, and ensure the jiggle pin (if present) is oriented as specified in the service manual. Clean the mating surfaces carefully—no gouges—and tighten the housing bolts evenly to the factory torque spec. Don’t overtighten, these are small fasteners into alloy.

After refitting, bleed the cooling system properly: heater on hot, use a fill funnel, squeeze the hoses to purge air, and run the engine until the fans cycle, topping up as needed. Use the correct Subaru-approved coolant (the blue Super Coolant or an equivalent that meets the same spec) mixed to the right ratio. If access under the car isn’t your thing—there’s an undertray to remove and a fair bit of coolant about—hand the job to a trusted mechanic for a tidy, leak-free result.

Popular questions about the 2010 Subaru Impreza thermostat housing

Where is the thermostat housing located on a 2010 Impreza?
It’s at the front lower side of the engine, bolted to the water pump, where the lower radiator hose attaches. Access is usually from underneath after removing the undertray.

Do I have to replace the housing when changing the thermostat?
Not always. If the housing’s sealing face is clean and flat and the hose neck isn’t cracked, it can be reused with a new O-ring. Replace the housing if it’s warped, pitted, or damaged.

What coolant should be used after replacing the thermostat/housing?
Use Subaru-approved Long-Life/Super Coolant (commonly the blue formulation) or an equivalent meeting the same spec. Don’t mix coolant types, flush if unsure, then refill and bleed thoroughly.