Parts for your 2020 Subaru Legacy-Radiator cap

2020 Subaru Legacy radiator cap – what’s actually fitted

Based on Subaru technical documentation, a traditional radiator-mounted cap is not used on the 2020 Subaru Legacy. The BT-series Legacy (FB25 and FA24 engines) runs a sealed, pressurised cooling system that places the pressure cap on a separate header/expansion tank rather than on the radiator neck. Subaru’s 2020 Legacy/Outback Service Manual (Engine Cooling) specifies filling and bleeding via the reservoir cap, and the Subaru electronic parts catalogue lists a “reservoir tank cap” with no cap on the radiator itself. The 2020 Owner’s Manual also directs owners to never open the coolant reservoir cap when hot and to fill at the tank, reinforcing that the radiator has no user-serviceable cap.

Why the change? Mounting the pressure cap on a high-mounted header tank keeps the fill point at the system’s highest spot under the bonnet. That makes air purging more reliable, improves coolant deaeration during operation, and suits the low-profile radiator packaging used on the Subaru Global Platform. With the radiator top sitting lower than the engine, a cap on the radiator would trap air, a header tank with cap solves that and simplifies service procedures.

What should owners service instead? The correct focus is the coolant reservoir/header tank cap — it’s the pressure cap that controls system pressure and vacuum recovery. Most non‑turbo 2020 Legacy models use a cap around 1.1 bar (≈108 kPa), while some turbo variants run a higher rating. Always match the rating printed on the cap or specified in the parts catalogue for the exact VIN.

Good practice under Australian and New Zealand conditions is to:

• Inspect the reservoir cap at least annually or every 15,000 km: check the rubber seals for nicks or hardening and ensure the spring moves smoothly.
• Replace the cap if there’s evidence of coolant crusting near the cap, hoses collapsing as the engine cools (failed vacuum valve), unexplained coolant loss, or temperature creep on long climbs.
• Use a genuine or high‑quality cap meeting Subaru’s pressure spec, and only remove it stone cold, using a rag to protect from residual pressure.
• During coolant service, follow Subaru’s fill/bleed steps via the reservoir cap and use Subaru‑approved premixed coolant.

If a “radiator cap” is listed generically by parts stores for this model year, they’re almost always referring to the pressurised reservoir/header tank cap, not a cap on the radiator itself.

Popular questions

Does the 2020 Subaru Legacy actually have a radiator cap?
Yes and no. It doesn’t have a cap on the radiator neck, but it does have a pressure cap on the coolant header/expansion tank. That cap is the one to check, service, or replace.

What pressure rating should the cap be on a 2020 Legacy?
Most non‑turbo FB25 cars use about 1.1 bar (≈108 kPa). Turbo variants may specify a higher rating. Confirm the exact rating on the cap label or via a Subaru parts lookup for the vehicle’s VIN.

How often should the cap be replaced?
Have it inspected at regular services. Replace if seals are perished, the vacuum valve sticks, or whenever cooling system work is performed and the cap shows age. Many techs opt to renew it alongside a major coolant service.