Parts for your 2010 Subaru Impreza-Radiator cap

2010 Subaru Impreza radiator cap — what it does, where it lives, and when to replace it

Based on the Subaru Factory Service Manual (2010MY Impreza, Cooling section), the Subaru genuine parts catalogue, and the Owner’s Manual safety notes, a pressure-type radiator cap is absolutely used on the 2010 Subaru Impreza. On naturally aspirated models, the cap sits on the radiator neck. On turbo variants (WRX/STI), the pressurised cap is on the alloy header/expansion tank near the intake manifold, and the radiator itself may not have a cap. So the “radiator cap” is a relevant part for all 2010 Impreza models, though its exact location depends on the engine.

The cap’s job is simple but critical: it seals and pressurises the cooling system so coolant can run hotter without boiling, keeping the boxer engine happy under Aussie and Kiwi conditions. Inside the cap is a spring-loaded pressure valve that holds pressure to a set rating, plus a vacuum valve that lets coolant draw back from the overflow bottle as things cool down. If that balance goes off, they’ll often see coolant loss, gurgling, or a heater that plays up.

For servicing, the best approach is to match the cap’s pressure rating and neck style exactly. The rating is printed on the cap, naturally aspirated models commonly use around 1.1 bar, while some turbo variants run higher. Don’t guess—check the existing cap, the bonnet decal, or the workshop data. Mixing ratings can invite overheating or hose stress.

• Replace the cap if the rubber seals are cracked, the spring feels weak, or there’s crusty residue around the neck.
• As a rule of thumb, test or replace the cap every 4–6 years or 80,000–100,000 km, or any time the cooling system is opened.
• Always remove the cap only when the engine is stone-cold, cracking it hot can cause a scalding coolant spray.

On a WRX/STI, remember the pressurised cap is on the header tank. If fitting a new cap there, also inspect the non-pressurised overflow bottle and hose for brittleness. On non-turbo models, inspect the radiator neck for nicks that can stop a good seal. Use quality coolant at the correct spec, bleed air properly after any cooling work, and keep an eye on these tell-tales of a dodgy cap:

• Coolant smell, damp spots, or white crust near the cap area
• Overheating in traffic but fine on the open road
• Upper hose collapsed after cool-down, or the overflow bottle not returning coolant

Get the cap right and the Impreza’s cooling system stays stable, the heater works as it should, and weekend drives are drama-free.

Popular questions

Where is the radiator cap on a 2010 Subaru Impreza?
Naturally aspirated models have the cap on the radiator itself. WRX/STI models place the pressurised cap on the alloy header/expansion tank near the intake manifold, and the radiator may have no cap. If they can’t spot it on the radiator, look for the small alloy tank high in the engine bay.

What pressure rating cap should be used?
Match the original rating shown on the existing cap or the bonnet decal. Many non‑turbo cars use around 1.1 bar, while some turbo variants run a higher rating. Using the wrong rating can cause premature boiling, hose stress, or persistent coolant loss.

Can a faulty cap cause overheating?
Yes. A weak or leaking cap drops system pressure, lowering the coolant’s boiling point. That can lead to overheating in stop‑start traffic, gurgling noises, inconsistent cabin heat, and spills from the overflow bottle.