Parts for your 2010 Subaru Forester-Radiator cap

2010 Subaru Forester radiator cap — what it does and when to replace it

Based on the Subaru Factory Service Manual for the 2010 Forester (Cooling section) and major parts catalogues from OEM and aftermarket suppliers, the 2010 Subaru Forester is fitted with a pressurised radiator cap (also called a pressure cap). The manual specifies a cap opening pressure of around 108 kPa (1.1 bar) and includes inspection procedures, confirming the part is relevant to this model. On non‑turbo Foresters the cap sits on the radiator neck, Turbo (XT) variants place the pressure cap on the engine’s coolant filler/header tank.

The radiator cap on a 2010 Forester quietly does a big job. It seals the cooling system so it can build pressure as the engine warms up, lifting the coolant’s boiling point and helping prevent overheating on long climbs, hot days, or when towing. Inside the cap are two valves: a pressure valve that holds pressure to its rated limit, and a vacuum valve that lets coolant flow back from the overflow bottle as things cool down, keeping the system topped up without air pockets.

As part of routine servicing, the cap deserves a quick once‑over. Look for brittle or cracked rubber seals, corrosion on the spring or seat, and any dried coolant crust around the neck. If there are cooling issues like random temperature swings, soft hoses that collapse after cool‑down, or the overflow bottle overfilling and not returning, the cap is a usual suspect.

When replacing, stick to the correct pressure spec (about 108 kPa unless your specific engine variant calls for otherwise) and buy an OEM cap or a high‑quality equivalent. Cheap universal caps can open too early or stick shut, either of which can cause dramas. Only remove the cap when the engine is stone cold. Wipe the filler neck clean, make sure the overflow hose is clear, and refill with the correct Subaru long‑life coolant as per the under‑bonnet label or owner’s manual. It’s smart to test the cap during any coolant service and replace it if it doesn’t hold pressure on a tester, or proactively every few years/major services given our hotter Aussie and Kiwi conditions.

Handled right, a fresh, properly rated radiator cap helps the Forester run cooler, last longer, and keep its heater and demister working a treat.

FAQs

What pressure rating does a 2010 Forester radiator cap use?
Most 2010 Forester caps are rated around 108 kPa (1.1 bar), as noted in the Subaru service literature and parts catalogues. Some turbo variants may specify a different rating, so it’s best to confirm by VIN or the under‑bonnet label and match the cap to the original spec.

Where is the radiator cap on a 2010 Forester?
On non‑turbo models it’s on the radiator neck at the front of the engine bay. On turbo (XT) models, Subaru uses a pressurised header tank on the engine—so the cap is on that tank rather than the radiator itself. The overflow bottle remains non‑pressurised.

What are the signs of a failing radiator cap?
Common clues include overheating at highway speeds, coolant pushing into the overflow bottle and not returning, collapsing upper radiator hose when cold, and dry coolant residue around the cap. If a pressure test shows it won’t hold spec, replace it.