Parts for your 2009 Subaru Legacy-Radiator cap

2009 Subaru Legacy radiator cap — what it does and how to look after it

Based on Subaru’s technical documentation — including the 2009 Legacy/Outback Service Manual (Cooling section) and the official Subaru parts catalogue (which lists “Cap – Radiator” for 2009 Legacy variants, e.g., PN 45137AE001/45137AE003) — this model does use a radiator cap. On most EJ25 2.5-litre engines it sits on the pressurised coolant filler/header tank near the top of the engine rather than on the radiator itself, some H6 and other variants place the cap on the radiator neck. Either way, a serviceable pressure cap is part of the cooling system.

The radiator cap’s job is simple but vital: it seals the cooling system and controls pressure so the coolant’s boiling point is raised, helping the Legacy keep its cool on long Kiwi or Aussie drives. Inside the cap are pressure and vacuum valves. When the engine heats up, excess pressure vents to the overflow bottle, when it cools, the vacuum valve draws coolant back, keeping air out. A healthy cap prevents boil-over, hose collapse, and fluctuating temps — and it’s extra important on turbo models that run hotter.

For servicing, it’s smart to check the cap at every service interval (roughly every 10,000–15,000 km). Subaru’s workshop procedures specify pressure-testing the cap to its rating (commonly around 108 kPa/1.1 bar for many 2.5i models and up to 127–137 kPa/1.3 bar for some turbo or H6 variants — always match the rating printed on the old cap or the under-bonnet label). Replace the cap if it won’t hold pressure, the rubber seal is cracked or hard, the spring is weak, or there’s corrosion on the neck.

• Typical symptoms of a crook cap: coolant smell, brown crust around the filler neck, random overheating at highway speeds, coolant loss into the overflow, or upper hose collapse after cool-down.
• Quick tips: only open when stone cold, inspect and clean the neck, ensure the overflow hose is tight and clear, fit the new cap by pressing down and turning to the second stop.
• Replacement cadence: many owners swap caps proactively every 4–5 years, sooner in hot climates or if the test fails.

Using the correct, genuine-equivalent pressure rating matters. Too low and it can boil early, too high and it stresses hoses and the radiator. A good cap is cheap insurance for the 2009 Subaru Legacy’s heads, radiator, and heater core.

Popular questions about 2009 Subaru Legacy radiator caps

What pressure cap does a 2009 Legacy use?
Most 2.5i (EJ25) models use about 108 kPa (1.1 bar), while some turbo and H6 variants use around 127–137 kPa (1.3 bar). Check the stamping on your current cap, the under-bonnet label, or the Subaru part catalogue by VIN to be sure. Always match the rating to the engine variant.

Where is the radiator cap on a 2009 Legacy?
On many 2.5-litre models it’s on the pressurised coolant filler/header tank above the engine, not on the radiator itself. Certain H6 or other variants place the cap on the radiator neck. If you can’t see a cap on the radiator, look for the small alloy or plastic header tank with a pressure cap near the top of the engine bay.

How often should the cap be replaced?
Inspect and pressure-test at each service. Replace immediately if it fails the test or shows seal damage, and consider preventative replacement every 4–5 years. A fresh, correct-rating cap helps keep temps stable and avoids costly overheating dramas.