Parts for your 2009 Subaru Impreza-Radiator cap

2009 Subaru Impreza radiator cap — purpose and service tips

Based on Subaru technical literature, a pressure cap is indeed used on the 2009 Subaru Impreza. The Subaru Owner’s Manual (2009MY Impreza, Cooling System section) and the Subaru Service Manual (2009MY Impreza GE/GH/GR, Cooling/CO section) show a conventional radiator cap on naturally aspirated models, while WRX and STI variants use the same style pressure cap on the engine-mounted coolant filler/header tank instead of the radiator neck. Subaru’s electronic parts catalogue for 2009 Impreza also lists a serviceable pressure cap for these variants. So, whether it sits on the radiator or the header tank, the cap is relevant across the range.

On a 2009 Impreza, the radiator cap’s job is to hold pressure in the cooling system. By raising the boiling point of the coolant, it helps the engine keep its cool on hot Aussie and Kiwi days, long climbs, or when stuck in traffic. The cap also manages coolant flow to and from the overflow bottle as things heat up and cool down, preventing air pockets.

As part of regular servicing, the cap deserves a look-in. A weak spring, hardened seal or corroded seat can lead to overheating, coolant loss or a collapsed upper hose after shutdown. It’s smart to inspect the cap at every service and replace it if there’s cracking, perishing, a sticky valve, or if it fails a pressure test. Stick with the correct pressure rating specified for the VIN, turbo and non‑turbo models can differ, and fitting the wrong rating can invite dramas.

• Only remove the cap when the engine is completely cold.
• Check the rubber seals for nicks or flattening and the neck for corrosion or crusty deposits.
• If topping up, use the correct Subaru‑spec coolant mix and bleed the system properly to avoid airlocks.
• As a rule of thumb, replace the cap every 4–6 years or 80–100,000 km, sooner if symptoms appear.

Typical warning signs include slow overheating at highway speeds, coolant smell or stains near the cap, frequent top‑ups, or a heater that goes cold then hot. For WRX/STI owners, remember the cap is on the header tank under the bonnet, not the radiator itself—same part type, different location.

FAQs

Where is the radiator cap on a 2009 Subaru Impreza?
On naturally aspirated models it’s on the radiator neck. On WRX and STI models it’s on the engine-mounted coolant filler/header tank. Either way, it’s the same style pressure cap managing system pressure and coolant recovery.

What pressure rating cap should be used?
Use the pressure rating specified for your exact model and VIN. Non‑turbo cars commonly use a different rating to WRX/STI variants. Check the existing cap’s marking or the service manual and match like-for-like to maintain correct boiling point and system protection.

How often should the cap be replaced?
Inspect at every service and replace about every 4–6 years or 80–100,000 km, or immediately if it fails a pressure test or shows damaged seals, corrosion, or sticking valves. Preventative replacement is cheap insurance against overheating.