Parts for your 2013 Subaru Impreza-Thermostat

2013 Subaru Impreza Thermostat — What it does and when to replace it

Based on technical references — the Subaru factory service manual for the 2012–2016 Impreza (FB20 engine) and the Subaru electronic parts catalogue — the 2013 Subaru Impreza does use a conventional engine coolant thermostat. It’s a wax‑pellet style unit mounted in the water pump outlet housing, controlling coolant flow and typically beginning to open around 88°C.

On this Impreza, the thermostat’s job is to help the FB20 warm up quickly, then hold a steady operating temperature for good fuel economy, solid heater performance, and long engine life. When it’s shut, coolant recirculates within the engine so it gets up to temp faster. As it reaches its rated temperature, it opens and sends coolant through the radiator to shed heat. Running without a thermostat, or with a faulty one, can cause slow warm‑up, higher emissions, poor cabin heat, overheating, and even engine damage — so it’s a small part with a big say in how the car behaves.

Thermostats generally aren’t a routine “every service” item, but on a 2013 Impreza they’re often replaced proactively during cooling system work or when symptoms show up. Many workshops in Australia and New Zealand will suggest replacement during a timing cover/water pump job, or at higher mileage as cheap insurance, especially in hotter climates or if the vehicle tows.

• Common symptoms it’s due: engine takes ages to warm up, fluctuating temp gauge, overheating under load, weak cabin heat, cooling fans cycling oddly, or a P0128 code.
• Best practice: use a genuine‑spec thermostat with the correct temperature rating and new O‑ring, fit it with the jiggle valve oriented as per the service manual, refill with Subaru Super Coolant (blue, pre‑mix) or an approved equivalent.
• Bleeding tip: set the heater to HOT, run the engine with a spill‑free funnel, and watch for steady heat from the vents and a stable upper radiator hose temperature. Check the level again after the first proper drive.

If the housing is removed, clean the mating surfaces carefully and follow the factory torque specs for the bolts. After replacement, keep an eye over the next week for any drips, sweet coolant smell, or creeping temps. Done right, the new thermostat should deliver quick warm‑ups and rock‑steady temps for years.

Popular questions about 2013 Subaru Impreza thermostats

Where is the thermostat located?
It sits in the water pump outlet housing at the front of the engine, behind the lower radiator hose. From under the front bumper, follow the lower hose to the pump housing and you’re on it.

What temperature does it open?
The OEM‑spec unit typically starts opening around 88°C and is fully open near the low 100s°C. That balance keeps warm‑up quick while preventing overheating in Aussie and Kiwi conditions.

Should it be replaced during a coolant change?
Not mandatory, but wise if the car has high kilometres, there are any temperature irregularities, or you’re already doing water pump work. Always replace the O‑ring and use the correct coolant.