Parts for your 2008 Mitsubishi Outlander-Radiator cap

2008 Mitsubishi Outlander radiator cap — what it does and how to look after it

Based on Mitsubishi Motors’ factory service information for the CW‑series Outlander (2007–2010) and the associated parts catalogue, the 2008 Mitsubishi Outlander is fitted with a serviceable pressure radiator cap as part of its closed cooling system. It’s a standard component on both four‑cylinder and V6 variants and is designed to be inspected and replaced when worn.

The radiator cap isn’t just a lid — it’s a pressure regulator and vacuum valve in one. By holding the system at a set pressure (typically around 1.1 bar / ~16 psi), it raises the coolant’s boiling point so the Outlander can run efficiently on hot Aussie and Kiwi days without boiling over. As the engine cools, the cap’s vacuum valve allows coolant to return from the overflow bottle, keeping the system full and free of air pockets.

As part of routine servicing on a 2008 Outlander, the radiator cap deserves a quick once‑over. If the rubber seal is hardened or cracked, the spring feels weak, or the cap shows corrosion or crusty deposits, it’s time to swap it. A weak cap can cause creeping temperature at highway speeds, coolant loss, or coolant being pushed into the bottle and not drawing back as the engine cools. Go for a quality cap that matches the original pressure rating, using one that’s too low can invite overheating, while too high can stress hoses, the radiator, or the heater core.

Where is it? On most CW‑series Outlanders sold in Australia and New Zealand, the pressure cap sits on the radiator neck near the top tank. Some variants place the pressure cap on a filler neck in the upper hose circuit, but the principle is the same — that’s the one that holds pressure. The translucent plastic bottle alongside the radiator is for expansion and top‑ups only.

1. Only open the cap when the engine is stone cold. Pop the bonnet, use a rag, and crack it slowly to release any residual pressure.
2. Inspect the rubber seal, centre valve, and seating surfaces. Clean the filler neck and check for nicks.
3. Replace the cap if there’s any doubt, matching the pressure rating on the original label (commonly ~1.1 bar).
4. After replacement, top up with the correct premixed coolant and bleed air as specified. A quick pressure test to spec is a smart move.

Popular questions

Where is the radiator cap on a 2008 Mitsubishi Outlander?
On most Aussie and Kiwi 2008 Outlanders it’s on the top of the radiator, typically towards the left‑hand side as you face the vehicle. Some engine variants use a pressure cap on a separate filler neck in the upper hose circuit. The overflow bottle cap is not the pressure cap.

What pressure rating cap does it use?
Most 2008 Outlanders use a cap rated around 1.1 bar (about 16 psi). Check the stamping on your existing cap or the under‑bonnet label to confirm. Stick with the specified rating — too low can encourage boil‑over, too high can over‑stress the cooling system.

How often should the radiator cap be replaced?
There isn’t a strict kilometre interval, but it should be inspected at every service. Replace it at the first sign of a hardened seal, corrosion, weak spring action, or symptoms like coolant not returning from the bottle or a collapsed upper hose when cold. Many owners proactively replace the cap every few years to keep the cooling system in top nick.