Parts for your 2015 Subaru Xv-Radiator cap

2015 Subaru XV radiator cap — what it does, where it is, and when to replace it

Per Subaru technical literature, the 2015 Subaru XV does use a pressure radiator cap. The 2015 XV Owner’s Manual (Cooling/Engine coolant section), the Subaru Service Manual for the FB20 engine (Radiator Cap Inspection), and Subaru’s electronic parts catalogue all list a radiator/pressure cap for this model, with an opening pressure of about 108 kPa (1.1 bar), commonly supplied as Subaru part number 45137AE001 in AU/NZ markets. On the XV, the pressure cap is mounted on the high-point coolant filler tank (header tank) in the engine bay, not on the translucent overflow bottle.

That cap plays a bigger role than most drivers reckon. It seals the cooling system and holds pressure so the coolant’s boiling point is lifted, which helps keep temperatures steady on hot days, steep climbs, or long motorway runs. Inside the cap are two valves: a pressure valve that releases excess pressure to the overflow bottle, and a vacuum valve that draws coolant back in as the engine cools. Together they stop boil-over, prevent hose collapse on cool-down, and keep the system topped up.

As part of regular servicing on a 2015 Subaru XV, the cap is worth a proper look. A tired cap can mimic a failing radiator or water pump by letting coolant escape or air sneak in. Many workshops test it with a cap tester, if it won’t hold around 108 kPa or won’t pull vacuum, it’s time for a new one. Using the correct 1.1 bar spec is important—too low and the engine can overheat, too high and hoses or the radiator can be stressed.

• Typical replacement interval: 4–5 years or 80,000–100,000 km, or whenever testing fails.
• Quick checks: look for brittle or swollen rubber seals, a sticky spring, crusty deposits on the filler neck, or coolant odour near the cap.
• Symptoms of a dodgy cap: rising temps at highway speed, coolant loss with a full overflow bottle, collapsed upper hose after cool-down, weak cabin heat, or bubbles returning to the bottle.

If replacing, always start with a stone-cold engine. Remove the old cap, clean the filler neck, fit the new 1.1 bar cap, and ensure coolant is at the proper level in the filler tank and overflow bottle. After any cooling system work, run the engine with the heater on hot to purge air. Sticking with genuine Subaru Super Coolant (premix) and an OE-spec cap keeps the XV’s FB20 engine happy across Aussie and Kiwi conditions.

Where is the radiator cap on a 2015 Subaru XV?

On this model it sits on the metal coolant filler tank (also called the header tank) positioned high in the engine bay, not on the plastic overflow reservoir. The overflow bottle is not pressurised, the cap on the filler tank is the system’s pressure cap.

What pressure cap does the 2015 XV need?

Subaru specifies an opening pressure of approximately 108 kPa (1.1 bar) for the XV with the FB20 engine. Sticking to the OE rating helps maintain the correct boiling point and system balance.

Can a bad radiator cap cause overheating or coolant loss?

Yes. A weak cap can let coolant push out to the overflow early or draw air back in as the engine cools, leading to overheating, fluctuating temps, or a low filler tank even when the overflow looks normal. Testing or swapping in a known-good 1.1 bar cap is a quick diagnostic step.