Parts for your 2020 Subaru Impreza-Radiator cap

2020 Subaru Impreza radiator cap — what it does and how to look after it

Based on Subaru’s own technical literature — the 2020 Impreza Owner’s Manual and the factory Service Manual available via Subaru TechInfo — this model does use a pressurised radiator cap. It’s fitted to the pressurised filler neck/header tank near the top of the engine, and should not be confused with the translucent overflow/reserve bottle, which is not pressurised.

The radiator cap isn’t just a lid — it’s a precision pressure valve. By holding a set pressure (typically around 108 kPa or 1.1 bar for many Subaru FB-series engines, always check the stamping on your cap or the service data for your VIN), it raises the coolant’s boiling point and helps move coolant between the radiator and overflow bottle as the engine heats and cools. The vacuum valve in the cap draws coolant back as things contract, preventing collapsed hoses and keeping the system topped up.

As part of regular servicing on a 2020 Subaru Impreza, the cap deserves a quick look. Under the bonnet and only when stone cold, check the rubber seal for nicks, flattening or hardening, confirm the spring feels firm, and make sure the filler neck is clean and free of corrosion or crusty deposits. A cooling system pressure test or a cap tester can confirm it still holds the specified kPa.

• Tell-tale signs of a crook cap: slow coolant loss with no obvious leak, overheating in traffic, heater going cold at idle, hoses collapsing as the engine cools, staining around the filler neck, or a cap that’s hard to remove or has a torn seal.
• Good practice: inspect at every service, replace any time the seal is suspect or the test result is out of spec, and consider fitting a new cap when you change coolant.

When replacing, use a genuine Subaru cap or a high-quality equivalent that exactly matches the pressure rating and neck type. To remove the cap safely, wait until completely cold, place a rag over the cap, and turn slowly to the first stop to vent any residual pressure before removing. Refill with the correct Subaru-approved coolant mix and bleed the system properly to avoid air pockets.

Look after the cap and it’ll look after the rest of the cooling system — simple as.

Popular questions about the 2020 Subaru Impreza radiator cap

Where is the radiator cap on a 2020 Subaru Impreza?
It’s on the pressurised filler neck/header tank near the top of the engine, not on the overflow bottle. On right-hand-drive cars, you’ll typically find it toward the front-right side under the bonnet. Always open only when the engine is completely cold.

What pressure rating does the 2020 Impreza radiator cap use?
Most 2020 Impreza models with the FB20 engine use a cap around 108 kPa (1.1 bar). Check the number stamped on your existing cap or the Subaru service data for your VIN to be sure. Using the wrong pressure rating can affect cooling performance and system longevity.

How often should the radiator cap be replaced?
Have it inspected at each service and replace it if the seal is worn, the spring’s weak, it fails a pressure test, or any time you’re doing cooling system work and want preventative peace of mind. Many owners choose to renew the cap proactively every few years to avoid hassles.