Parts for your 2009 Mitsubishi Outlander-Radiator cap

2009 Mitsubishi Outlander radiator cap — what it does and when to replace it

For the 2009 Mitsubishi Outlander (CW series, 4B12 2.4 petrol and 6B31 3.0 V6), a radiator cap is fitted to the radiator’s top tank and is part of the pressurised cooling system. This is confirmed by Mitsubishi’s factory Service Manual for 2007–2010 Outlander Cooling System (radiator cap inspection and relief-pressure spec 108–137 kPa/1.1–1.4 bar), the Mitsubishi ASA parts catalogue listings for CW5W/CW6W models (radiator cap, 1.1 bar), and aftermarket catalogues for the OE-style Denso radiator that show a cap-equipped radiator.

The cap’s job is simple but critical. It seals the system so coolant can run at a controlled pressure, raising the boiling point and helping the Outlander keep its cool in Aussie and Kiwi conditions. Inside the cap are a spring-loaded pressure valve and a vacuum valve. Under heat, excess pressure vents to the overflow bottle, as things cool, the vacuum valve draws coolant back, keeping air out. A tired cap can cause slow coolant loss, overheating in traffic, or collapsed hoses after cooldown.

As part of any routine service, it’s smart to check the radiator cap condition under a cold bonnet. Look for perished rubber seals, a sticky spring, crusty deposits, or a distorted seat. If available, test the cap with a pressure tester to the spec stamped on the cap (typically 1.1 bar for this model). Replace the cap if it won’t hold pressure or if it’s more than a few years old. Many workshops in Australia and New Zealand treat a radiator cap as low-cost insurance—inspect at each service interval (around 10,000–15,000 km) and consider replacement at 5–7 years or any time symptoms appear.

When replacing, choose an OEM or quality equivalent cap with the correct pressure rating. Only remove the cap when the engine is completely cold: use a rag, press down and turn to the first stop to bleed any residual pressure, then remove fully. After refitting, top up with the correct coolant, run the engine with the heater on high, and check for bubbles or level drop. The Outlander’s plastic overflow bottle has a non-pressurised lid, the radiator cap is the system’s actual pressure control device, so it needs to be right for the cooling system to behave.

• Common signs of a failing cap: unexplained coolant loss, overheating at idle, collapsed upper hose when cold, white crust at the filler neck, or coolant pushed into the overflow and not returning.

Popular questions about 2009 Mitsubishi Outlander radiator caps

What pressure cap does a 2009 Outlander use?
Most 2009 Outlanders run a 1.1 bar (about 108 kPa) radiator cap, as noted in Mitsubishi service data and typical OEM caps for CW-series models. Always confirm by reading the stamping on the existing cap or checking the VIN in a parts catalogue, as regional variations can exist.

How can someone test their radiator cap at home?
With the engine cold, a hand-held cap pressure tester can be used to pressurise the cap to its rated value. If it can’t hold pressure or releases too early/late, replace it. Also inspect the rubber seal and the spring for wear. If a tester isn’t available, many workshops offer a quick cap test during a cooling-system check.

Does the Outlander have a pressurised expansion tank?
No. On this model the overflow reservoir is non-pressurised with a simple plastic lid. The radiator cap mounted on the radiator itself is the pressure-control component for the entire cooling system.