Parts for your 2017 Subaru Forester-Radiator cap

2017 Subaru Forester radiator-cap — what it does and where it lives

Technical sources confirm the 2017 Subaru Forester (SJ series, FB25/FA20 engines) does use a pressure radiator-cap, but it’s mounted on the coolant filler/header tank rather than on the radiator itself. The 2017 Forester Owner’s Manual refers to the “coolant filler tank cap” and cautions against removing it when hot. The Subaru Workshop/Service Manual (Cooling System section) specifies the cap’s opening pressure at about 108 kPa (1.1 bar) and outlines inspection steps. Subaru’s parts catalogue lists a “Cap – Radiator” for this model (e.g., P/N 45137AE000/45137AE001). So, even though the radiator neck doesn’t carry a cap, the vehicle absolutely relies on a radiator-cap as part of its pressurised cooling system.

On the 2017 Forester, the radiator-cap’s job is to keep the cooling system sealed and pressurised so the coolant can run hotter without boiling, improving engine temperature control under Aussie and Kiwi conditions. It’s a small part that does plenty: it holds pressure to the rated spec, lets excess coolant flow to the overflow bottle when things heat up, and draws coolant back as the system cools. Subaru locates the cap on the high-mounted coolant filler/header tank under the bonnet, making it the highest point in the system for proper bleeding and top-ups.

As part of routine servicing, it’s worth giving the cap a once-over. If its spring weakens or the seals harden, the system may lose pressure, which can show up as slow warm-up, overflow bottle bubbling, collapsing hoses, or a sweet coolant smell. A healthy cap rated to around 108 kPa (1.1 bar) is the go-to spec for this model—stick with OEM or equivalent quality.

• Only remove the cap when the engine is stone-cold. Twist to the first stop to vent any residual pressure.
• Inspect the rubber seals and the spring-loaded valve. Replace the cap if the seal is cracked, flattened, or the spring action feels lazy.
• Check the filler neck for nicks or scale, clean gently so the seal can seat properly.
• Top up with Subaru Super Coolant (blue, pre-mix) to the correct level, and ensure the overflow hose is tight and crack-free.
• If coolant is being renewed (Subaru’s long-life coolant often goes 11 years/220,000 km), consider fitting a fresh cap at the same time for peace of mind.

A quick cap replacement is inexpensive insurance against overheating or air ingress. For anyone touring long distances or towing, carrying a spare quality cap is a smart move.

1. Where is the radiator-cap on a 2017 Subaru Forester?

   It’s on the coolant filler/header tank, not on the radiator neck. Subaru places it at the system’s highest point to make bleeding and top-ups easier and to keep the system properly pressurised.

2. What pressure rating cap should be used?

   Use a cap around 108 kPa (1.1 bar), the common Subaru spec for this model. Match the rating printed on your original cap and choose OEM or equivalent quality.

3. How often should the radiator-cap be replaced?

   There’s no strict kilometre interval, but it should be inspected at every service. Many techs replace the cap proactively every 4–5 years or when changing coolant, or immediately if there are signs of pressure loss, hardened seals, or overheating symptoms.