Parts for your 2010 Subaru Impreza-Thermostat

2010 Subaru Impreza Thermostat — What It Does, When to Replace, and How It’s Looked After

Technical sources confirm the 2010 Subaru Impreza is fitted with an engine coolant thermostat. The Subaru Factory Service Manual for 2010MY Impreza (GE/GH/GR/GV) in the Cooling System section specifies a wax‑pellet thermostat installed in the water pump housing (lower radiator hose side), with a start‑to‑open temperature around 78°C and the jiggle valve oriented at the top. The Subaru Genuine Parts Catalogue lists a dedicated thermostat assembly and seal for the EJ‑series engines used in this model year. Independent catalogues (e.g., Gates and Dayco) also publish direct‑fit thermostat listings for the 2010 Impreza. These technical references make it clear the thermostat is a standard, relevant component on this vehicle.

The thermostat on a 2010 Subaru Impreza quietly manages engine temperature so the car warms up quickly and then holds a steady, efficient operating temp. That steadiness keeps fuel use in check, helps the heater work properly on cold mornings, and protects the engine from both over‑cooling and overheating. On these EJ engines, the thermostat lives in the water pump housing at the lower radiator hose, and it’s designed to open at roughly 78°C, then modulate flow through the radiator as load and ambient temp change.

Owners typically consider replacement when tell‑tale signs show up. Common clues include slow warm‑up or temp fluctuating on the gauge, poor cabin heat, overheating under load, radiator fans running more than usual, or coolant backing up into the overflow. Because access to the thermostat overlaps with cooling‑system work, many technicians recommend replacing it proactively when doing a water pump, timing belt, or major coolant service on higher‑kilometre cars. Sticking with a genuine‑spec thermostat and the correct seal is smart—these engines can be fussy about flow characteristics, and cheap units may run too cool or open inconsistently.

• Good servicing practice: refresh coolant at the recommended interval using the correct Subaru‑approved long‑life coolant, inspect hoses and clamps, and check for any crusty deposits around the thermostat housing.
• When fitting: install the new thermostat with the jiggle pin at 12 o’clock, seat the seal properly, tighten housing fasteners to factory spec, then refill and bleed the system carefully to purge air.
• Afterwards: run the engine to operating temp with the heater on, confirm steady gauge behaviour, check for leaks, and top up the reservoir once it cools.

Done right, a fresh, correct‑spec thermostat helps the Impreza feel crisp off the mark, keeps temps rock‑steady on the motorway, and gives the engine an easier life in Aussie and Kiwi conditions.

Popular questions about the 2010 Subaru Impreza thermostat

What temperature does the 2010 Impreza thermostat open?
The factory spec is roughly 78°C for start‑to‑open, with full opening reached higher up the scale. That range lets the EJ engine get up to proper operating temperature quickly and then hold it steady for performance, economy, and heater output.

Where is the thermostat on a 2010 Impreza?
It’s mounted in the water pump housing on the lower radiator hose side of the engine. The housing is secured with a couple of bolts