Parts for your 2009 Honda Stream-Radiator cap

2009 Honda Stream radiator cap: fitment, purpose and servicing tips

Technical references including Honda’s workshop information for the RN6–RN9 Stream range (2006–2014) and the Honda Genuine Parts Catalogue confirm that the 2009 Honda Stream is fitted with a spring‑loaded radiator pressure cap. The cap is typically rated at 1.1 bar and mounted on the engine-side filler neck rather than on the translucent overflow bottle. Common Honda listings show “Cap, Radiator (1.1)” used across R18A and R20A Stream variants.

The radiator cap on a 2009 Honda Stream does more than just close a hole. It seals and pressurises the cooling system so coolant can run hotter without boiling, which helps the engine keep its cool on long Kiwi and Aussie drives. Inside the cap are two valves: one releases pressure to the overflow tank as coolant expands, and the other draws coolant back in as things cool down, keeping the system topped up and free of air. It’s also the proper fill point for coolant on this model, so it matters for bleeding and refills after a flush.

Owners should treat the radiator cap as a service item. A tired spring or perished rubber seal can lead to slow coolant loss, hard or collapsing hoses after cooldown, random temp spikes, or crusty deposits around the filler neck. Best practice is to inspect it at every service, pressure-test it if there are any cooling niggles, and replace it every few years or at the first sign of trouble. Stick with the correct pressure rating (generally 1.1 bar for the Stream) to avoid stressing hoses or lowering the boiling point.

• Only remove the cap when the engine is stone cold. Wrap a rag around it and crack it slowly to release any residual pressure.
• Check the rubber seals for cracks, flattening or swelling, and make sure the neck is clean and free of corrosion.
• If overheating, unexplained coolant loss, or weak cabin heat appears, test the cap with a cooling-system cap tester.
• Use Honda‑approved long‑life coolant and follow the recommended change intervals, refill via the cap and bleed air properly.

On the Stream, the cap sits on the metal/plastic filler neck near the upper radiator hose under the bonnet. The radiator core itself may not have a cap, that’s normal—this engine-side cap is the pressure control point for the whole system.

Popular questions about the 2009 Honda Stream radiator cap

Where is the radiator cap on a 2009 Honda Stream?
It’s on the engine-side filler neck near the top radiator hose, not on the overflow bottle. Pop the bonnet and look for the silver cap with a warning label—typically on the left-hand side when facing the car.

What pressure rating should the cap be?
Most 2009 Stream models use a 1.1 bar cap. Always confirm by reading the stamping on the existing cap or checking Honda parts data against the VIN to ensure the correct rating.

How can someone tell if the cap is failing?
Signs include overheating at random, coolant pushing into the overflow and not returning, collapsed hoses after cooldown, and crusty white or rusty deposits at the filler neck. A quick pressure test will confirm it.