Parts for your 2015 Subaru Forester-Radiator cap

2015 Subaru Forester radiator cap — is there one?

For the 2015 Subaru Forester (SJ series), a traditional radiator-mounted cap isn’t used. Subaru’s cooling layout for both the 2.5i (FB25) and 2.0XT (FA20F) puts the pressure cap on an engine‑mounted coolant filler tank (also called a header tank), not on the radiator itself. This setup is documented in the Subaru Forester 2015 Service Manual (Cooling section for FB/FA engines), reflected in the Subaru FAST/EPC parts catalogue for the SJ Forester, and noted in general repair references like the Haynes manual for 2009–2018 Forester models.

Why skip the radiator cap? Subaru’s boxer engine sits low, while the engine‑mounted filler tank is positioned as the high point of the cooling system. That means the pressure cap is placed where air naturally collects and where coolant is best introduced and controlled. The radiator is a sealed unit, fed by hoses, and doesn’t need a cap of its own.

• Better air separation and bleeding: The header tank is the highest point, so purging air and cold-filling are simpler and more reliable.
• Consistent pressure control: The cap regulates system pressure at the true high point, improving warm‑up and reducing hot spots.
• Packaging and durability: A sealed radiator (no filler neck) reduces potential leak points, handy with plastic end tanks and tight frontal packaging.
• Service practicality: Accessing one cap under the bonnet is safer and more straightforward, with less chance of scalding at the radiator.

So, while owners often search for a “radiator cap”, the part they’re after on a 2015 Forester is the coolant filler tank pressure cap. Most 2.5i models use a 1.1 bar (108 kPa) cap, 2.0XT turbo models commonly run a higher rating (around 1.3–1.4 bar). Always confirm by VIN or read the stamping on the existing cap. Inspect the cap’s rubber seals and spring at regular services, replace if the seal is perished, there’s crusty deposit build‑up, or a pressure test says it’s not holding spec. Only remove the cap when the engine is completely cold.

Technical references (no links): Subaru Forester 2015 Service Manual (Cooling, FB/FA Engines), Subaru FAST/EPC parts catalogue for SJ Forester, Haynes Repair Manual, Subaru Forester 2009–2018.

FAQ 1: Where is the radiator cap on a 2015 Subaru Forester?

There isn’t one on the radiator. The pressure cap sits on the engine‑mounted coolant filler tank (header tank) near the top of the engine. That’s the only cap you remove for filling or bleeding the cooling system.

FAQ 2: What pressure rating cap does it use?

Most 2015 Forester 2.5i (FB25) models use a 1.1 bar (108 kPa) cap. The 2.0XT (FA20F turbo) typically uses a higher rating, around 1.3–1.4 bar. Check the number stamped on your current cap or verify by VIN to be sure you’ve got the right spec.

FAQ 3: When should the cap be replaced?

Have it inspected at routine services. Replace if the rubber seal is cracked or flattened, the spring feels weak, it fails a pressure test, or you’re chasing cooling issues like intermittent overheating, hard or collapsed hoses, or unexplained coolant loss. Many owners choose to renew the cap around the five‑year/100,000 km mark as preventative maintenance.