Parts for your 2006 Subaru Impreza-Thermostat

2006 Subaru Impreza Thermostat — Purpose, Care, and When to Replace

Based on OEM technical references — including the 2006MY Subaru Impreza Factory Service Manual (Cooling System), Subaru Technical Information System (STIS) parts diagrams, and OEM parts catalogues — the 2006 Subaru Impreza is fitted with an engine coolant thermostat. It sits in the housing at the water pump inlet on the lower radiator hose side. So yes, a thermostat is absolutely relevant and used on this model.

On a 2006 Impreza, the thermostat’s job is to help the engine warm up quickly and then hold it at a steady operating temperature. That stability means better fuel economy, stronger heater performance on cold mornings, cleaner emissions, and less engine wear. In normal driving it meters coolant flow between the block and radiator, opening as coolant gets hot and closing again as it cools. Most OE units begin opening around the high‑70s to low‑80s °C and are fully open in the low‑90s °C, always follow the spec for the exact engine code.

There’s no fixed service interval just for the thermostat, but it’s smart to replace it when doing a timing belt and water pump (common around 160,000 km) or any time the cooling system is apart. Symptoms of a crook thermostat include slow warm‑up, fluctuating temp gauge, poor cabin heat, overheating, or a P0128 code. If the gauge drops on the motorway but creeps up in traffic, that’s a classic sign it’s stuck open or shut.

• Use a genuine or OE‑equivalent thermostat and the correct sealing ring/O‑ring.
• Orient the jiggle valve/bleed pin as specified by Subaru when fitting.
• Refill with the correct Subaru‑approved coolant mix and bleed air thoroughly.

Replacement basics under the bonnet are straightforward: drain some coolant, remove the lower radiator hose and two housing bolts, swap in the new thermostat and seal, refit, then refill and bleed. Tighten fasteners to factory spec and check for leaks once warm. After a road test, recheck coolant level when cold. Skipping the bleed can leave air pockets that cause erratic temps or no heater, so take the time to burp the system with the heater on full hot.

Going for a lower‑temp “track” thermostat on a daily driver isn’t usually worth it, stick with the OE temperature rating for the best balance of drivability and longevity.

Popular question: What temperature thermostat does a 2006 Subaru Impreza use?
Most factory EJ‑series engines in 2006 Imprezas use a thermostat that begins opening around 78–82°C and is fully open near 90–95°C. Match the OE spec on the genuine part for your exact variant.

Popular question: Where is the thermostat on a 2006 Impreza?
It’s mounted at the water pump inlet, where the lower radiator hose connects. Access is typically from underneath, have a drain pan handy, and replace the O‑ring when refitting.

Popular question: Do thermostats need regular replacement?
They’re not strictly time‑based items, but replacing the thermostat with the water pump and timing belt — or any time there are temperature irregularities or a P0128 — is good preventative maintenance.