Parts for your 2018 Mitsubishi Outlander-Radiator cap

2018 Mitsubishi Outlander radiator cap: what it does and when to replace it

Based on Mitsubishi’s workshop information for the GF/ZE Outlander series (2015–2020) and the Mitsubishi ASA parts catalogue, the 2018 Outlander uses a pressurised cooling system with a dedicated pressure cap. On the petrol and diesel variants the pressure cap is fitted to the radiator neck, on the PHEV it’s integrated on the pressurised expansion/degas bottle. Aftermarket catalogues (e.g., Stant/Gates fitment guides) also list a cap for 2018 Outlander models, confirming it’s a relevant service item.

A radiator cap is more than a simple lid. It holds a set pressure (typically around 1.1 bar/108 kPa for Mitsubishi passenger cars), which raises the coolant’s boiling point and keeps temperatures stable when you’re cruising the motorway, towing, or inching along in city traffic. It also manages expansion and contraction, allowing coolant to move to and from the overflow bottle as the engine heats and cools, so the system stays topped up and free of excess air.

For a 2018 Outlander, keeping the cap in good nick helps prevent overheating, coolant loss, and hard-to-trace hot‑running issues. As part of regular servicing—especially when changing coolant—inspect the cap’s rubber seals for cracks or flattening, check the spring action, and look for crusty deposits on the sealing surfaces. If there’s any doubt, replace it, caps are inexpensive compared to the cost of a cooked engine.

Quick tips under the bonnet:

• Only remove the cap when the engine is completely cold. A hot system is under pressure and can spray scalding coolant.
• Verify the pressure rating on the new cap matches the original spec (around 1.1 bar for most trims). The wrong rating can cause leaks or premature hose/radiator failure.
• Clean the filler neck or bottle seat before refitting so the seal beds properly.
• If the cooling system has been opened, bleed any trapped air per the workshop procedure to avoid hot spots.

How often should it be replaced? Many techs in Australia and New Zealand treat the cap as a 4–5 year or 80,000–100,000 km item, or they replace it proactively whenever the coolant is renewed. If you notice recurring low coolant, sweet smells, overheating at idle, or collapsed hoses after cooldown, add the cap to the diagnostic checklist.

Where is the radiator cap on a 2018 Outlander?

On most petrol and diesel 2018 Outlanders, it’s on the radiator neck beneath the plastic upper cover. On the PHEV, the system uses a pressurised expansion/degas bottle with the pressure cap on the bottle instead of the radiator. Always verify by following the upper radiator hose to its fill point.

What pressure rating does the cap use?

Mitsubishi typically specifies about 1.1 bar (108 kPa) for the Outlander range of this era. Check the stamping on your existing cap or your owner’s manual/workshop data to match it exactly, especially if your vehicle tows or operates in hot conditions.

When should the radiator cap be replaced?

Replace at coolant change intervals or every 4–5 years/80,000–100,000 km, sooner if seals are cracked, the spring is weak, there are visible deposits, or if you’re chasing intermittent overheating or coolant loss. It’s a low-cost preventative fix that protects the entire cooling system.