Buy OEM 2021 Subaru Part # 45155XC00A. Cap Reserve Tank. Engine Coolant Expansion Tank A failed expansion tank can cause the cooling system in your 2021 Subaru to leak

CAP-RESERVE TANK Radiator Cap

Fits Ascent, Legacy, Outback

Engine Coolant Expansion Tank
A failed expansion tank can cause the cooling system in your 2021 Subaru to leak antifreeze, or it can cause your engine to overheat. If you're losing coolant, contact our service department to avoid engine damage.