Parts for your 2018 Subaru Xv-Radiator cap

2018 Subaru XV radiator cap: what it does and how to look after it

Yes, the 2018 Subaru XV absolutely uses a radiator cap. Technical references including the 2018 XV/Crosstrek Owner’s Manual (Cooling system section) and the Subaru Service Manual for the FB20 engine specify a pressurised cap mounted on the coolant filler tank under the bonnet, with a separate translucent overflow reservoir that has a non-pressurised cap. The service literature also notes a cap pressure around 108 kPa (about 1.1 bar), which is typical for Subaru’s naturally aspirated FB-series engines.

On this model, the radiator cap is a small but critical bit of kit. It seals the cooling system, holds pressure so the coolant’s boiling point is raised, and uses a spring-loaded relief valve to vent excess pressure to the overflow bottle when things get hot. As the engine cools, its vacuum valve draws coolant back from the reservoir to keep the system full. That pressure control helps prevent localised boiling, air pockets and overheating, while protecting hoses and the radiator from excessive stress.

For servicing a 2018 Subaru XV radiator cap, the goal is reliability and the right pressure. The cap’s rubber seals harden and the spring weakens with age, which can show up as hard-to-pin-down coolant loss, frequent gurgling, or the overflow bottle filling and not returning. Subaru guidance has the cap inspected at regular services (typically every 12 months/15,000 km in AU/NZ schedules), and pressure-tested if there are any cooling complaints. If the cap fails a pressure test, shows cracked seals, corrosion on the seat, or a sticky valve, replace it. Stick with the specified pressure rating, grabbing a higher-pressure aftermarket cap can stress hoses, the heater core and the radiator unnecessarily.

• Only open the cap when the engine is stone cold. Hot, pressurised coolant can cause serious burns.
• Check the sealing surfaces: clean any crusty deposits from the filler neck with a lint-free cloth.
• Inspect the overflow hose from the neck to the reservoir for splits or loose clamps, the vacuum return relies on it.
• If topping up, use the correct Subaru Super Coolant (or equivalent) mix and bleed air per the workshop procedure.
• Replace the cap proactively every 4–6 years or 80,000–100,000 km, or sooner if testing suggests it’s weak.

Look after the cap and it’ll look after the XV: stable temperatures, no random coolant dramas, and a happier FB20 on long Aussie and Kiwi drives.

FAQs

Does the 2018 Subaru XV actually have a radiator cap, and where is it?
Yes. It’s on the pressurised coolant filler tank under the bonnet, not on a separate header tank. You’ll also see a translucent overflow reservoir nearby, that one has a simple, non-pressurised cap. The pressurised cap is the one that sets system pressure and should only be opened when the engine is completely cold.

What pressure rating cap should be used on a 2018 Subaru XV?
Subaru specifies a cap around 108 kPa (about 1.1 bar) for the FB20 in the 2018 XV. Using the correct rating helps maintain the designed boiling margin without over-stressing hoses and the radiator. Avoid higher-pressure caps unless Subaru documentation for your exact VIN specifies otherwise.

How often should the radiator cap be replaced?
Have it inspected at every service and pressure-tested if there are any cooling symptoms. As a rule of thumb, many techs replace the cap every 4–6 years or 80,000–100,000 km. Replace sooner if you see cracked seals, corrosion, a stuck valve, or it fails a pressure test.