Parts for your 2012 Subaru Impreza-Radiator cap

2012 Subaru Impreza radiator cap — what it does, where it lives, and when to replace it

Per Subaru technical literature, a radiator cap is used on the 2012 Subaru Impreza. The 2012MY Impreza Factory Service Manual (Cooling System) and Subaru parts catalogues specify a pressurised cap fitted to the coolant filler tank (sometimes called the radiator filler tank or header tank) rather than the radiator neck itself. The Owner’s Manual cautions against opening the cap when hot, confirming its presence and role. So, while the radiator body is cap‑less, the system still relies on a proper radiator cap on the filler tank for correct operation.

On the 2012 Impreza (FB-series engine), the radiator cap’s job is simple but vital: it seals and pressurises the cooling system so coolant can run hotter without boiling, then manages expansion and contraction as temperatures swing. Inside the cap are pressure and vacuum valves. Under load, it holds a set pressure (typically around 1.1 bar/108 kPa as specified by Subaru) to lift the boiling point and keep things stable. As the engine cools, the vacuum valve opens to draw coolant back from the overflow, preventing air pockets and hose collapse.

Because Subaru routes the cap to a separate filler/header tank near the top of the engine bay, owners shouldn’t go hunting for a cap on the radiator itself. This layout helps purge air and makes top-ups easier under the bonnet. Fitment of the correct pressure rating matters, too low and it can boil or push coolant out early, too high and it can stress hoses, the heater core or gaskets.

As part of routine servicing, the cap deserves a quick once‑over. Look for hardened, cracked or swollen rubber seals, a sticky spring, white crust or rust on the seat, and signs of weeping around the neck. Common symptoms of a dodgy cap include slow coolant loss, intermittent overheating, a collapsed upper hose after cool‑down, or poor cabin heat on cold starts.

• Check the cap at each service interval and any time cooling work is done.
• Pressure‑test the cap if in doubt, replace if it won’t hold the rated pressure or won’t draw back.
• Only remove the cap when the engine is stone cold. Wrap a rag around it and crack it slowly to release any residual pressure.
• Refill and bleed per the Subaru service procedure, using the correct Subaru‑spec coolant and the specified cap rating.

A quality, OE‑spec cap is a cheap bit of insurance that keeps the Impreza’s cooling system happy for heaps of kilometres with no dramas.

Popular questions about the 2012 Subaru Impreza radiator cap

Where is the radiator cap on a 2012 Impreza?
It’s on the pressurised coolant filler/header tank, not on the radiator. Look near the top of the engine bay for a small plastic tank with the metal pressure cap on top.

What pressure rating does it use?
Subaru specifies roughly 1.1 bar (108 kPa) for this model. Always match the rating printed on the original cap or confirm against Subaru service information to avoid cooling issues.

How often should it be replaced?
Inspect at every service. Many owners replace the cap every 3–5 years, or immediately if it fails a pressure test, shows damaged seals, or there are symptoms like coolant loss or a collapsed hose after cool‑down.