Parts for your 2006 Subaru Impreza-Radiator cap

2006 Subaru Impreza radiator cap — what it does and when to replace it

Based on the Subaru Impreza 2006MY Factory Service Manual (Cooling System) and Subaru’s global parts catalogue, the 2006 Subaru Impreza does use a radiator cap. On non‑turbo models the cap is mounted on the radiator filler neck, while WRX/STI turbo models use a pressurised header tank (expansion tank) with the pressure cap located there. So the radiator cap is absolutely relevant to any 2006 Subaru Impreza.

The radiator cap is a small part that does a big job. It seals the cooling system and sets the pressure the system runs at, raising the coolant’s boiling point so the engine can handle Aussie heatwaves and Kiwi alpine climbs without boiling over. Inside the cap are a spring and valves that hold pressure to a set rating, then safely vent excess to the overflow bottle as things get hot. As the engine cools, the vacuum valve draws coolant back in, keeping air out and the system topped up.

For a 2006 Impreza, the correct cap typically sits around 0.9–1.1 bar (about 13–16 psi). Many WRX/STI caps are 1.1 bar, some non‑turbo models use around 0.9–1.1 bar depending on market. The right rating is printed on the cap and listed in the owner’s handbook and parts guide—matching that spec matters. A “high‑pressure racing” cap isn’t a free upgrade, too much pressure can stress radiators, hoses and gaskets.

Good servicing includes checking the radiator cap every service interval. Under the bonnet, look for brittle or flattened rubber seals, a sticky or wobbly spring, corrosion on the seat, or cracked plastic around the neck. If there’s coolant loss with no obvious leaks, hoses that collapse when cold, overflow bottle not returning coolant after shutdown, overheating at low speeds, or a heater that goes hot–cold, the cap is a prime suspect. Workshops can pressure‑test the cap, if it can’t hold its rated pressure or won’t pull a vacuum, it’s due for replacement.

Replacement is inexpensive and quick. Only remove the cap when the engine is stone cold, twist slowly with a rag to release any residual pressure, clean the filler neck, and fit a quality OEM‑spec cap. On turbo models with a pressurised header tank, focus on that cap—the plastic overflow bottle cap is not pressurised. Pair a fresh cap with correct Subaru‑spec coolant and proper bleeding to keep the 2006 Subaru Impreza happy for many kilometres.

• Technical references consulted: Subaru Impreza 2006MY Factory Service Manual (Cooling System), Subaru Global/FAST parts catalogue listings for 2006 Impreza radiator caps (common ratings ~0.9–1.1 bar), aftermarket catalogues from Gates and Denso for 2006 Impreza cap specifications.

Popular questions about 2006 Subaru Impreza radiator caps

What pressure rating should a 2006 Subaru Impreza radiator cap have?
Most 2006 Impreza models use a cap in the 0.9–1.1 bar range (about 13–16 psi). WRX/STI variants commonly run 1.1 bar, while non‑turbo models may be 0.9 or 1.1 bar depending on market and radiator/header tank setup. The exact rating is printed on the existing cap and listed in the owner’s handbook.

Always match the factory rating. Going higher can raise stress on hoses, radiators and gaskets without real‑world benefit for a road car.

How often should the radiator cap be replaced?
There’s no hard expiry date, but it’s smart to inspect the cap at every service and replace it at the first sign of weak spring pressure, cracked or flattened seals, corrosion, or failed pressure/vacuum tests. Many owners choose to renew the cap every 4–5 years as cheap insurance, especially before summer.

What are the signs of a failing radiator cap on a 2006 Impreza?
Typical symptoms include coolant pushing into the overflow bottle and not returning, hoses collapsing after cool‑down, intermittent overheating at low speed, a fluctuating heater, or unexplained coolant loss without visible leaks. Any of these warrant testing or replacing the cap.