Parts for your 2018 Mitsubishi Asx-Radiator cap

2018 Mitsubishi ASX radiator cap — what it does and how to look after it

Based on technical documentation, the 2018 Mitsubishi ASX does use a radiator pressure cap. The 2018 ASX Owner’s Manual warns against opening the radiator cap when hot, the Mitsubishi Motors Service Manual for the ASX/RVR/Outlander Sport platform details inspection and pressure testing of the cap, and the Mitsubishi ASA electronic parts catalogue lists a radiator pressure cap as a serviceable component for 2018 ASX variants. On most ASX models, the pressurised cap sits on the radiator filler neck, with a separate overflow bottle nearby.

The radiator cap’s job is more than just sealing the top of the radiator. It controls cooling system pressure so the coolant can run hotter without boiling, keeps air out as the engine cools and contracts, and manages overflow to and from the reservoir. A healthy cap helps prevent overheating, coolant loss, and collapsed hoses under the bonnet.

As part of routine servicing on a 2018 Mitsubishi ASX, it’s worth checking or replacing the cap. Use a cap that meets the factory spec pressure (commonly around 1.1 bar/108 kPa—confirm on the cap label or service info). A workshop can pressure-test the cap, otherwise, inspect the rubber seals for hardening, nicks, or flattening, check the spring feels firm, and ensure the vacuum valve moves freely. If the cap is original and the vehicle’s clocked up five or more years or 100,000 kilometres, replacement is cheap insurance.

• Only open the cap when the engine is stone cold.
• Cover it with a rag and twist slowly to the first stop to vent any residual pressure.
• Clean the filler neck seat so the seal can do its job.
• After topping up, run the heater on hot and bring the engine to operating temp to purge air.

Drivers should also keep an eye out for tell-tales of a crook cap:

• Coolant smell, staining or overflow bottle filling and not returning.
• Upper radiator hose collapsing as the engine cools.
• Gradual coolant loss with no obvious leaks, or flaky heater performance.

Stick with quality OEM or equivalent caps, match the pressure rating, and replace the cap whenever there’s doubt. It’s a small part that keeps the ASX’s cooling system sweet, especially on hot Aussie and Kiwi summer days.

FAQs

Where is the radiator cap on a 2018 Mitsubishi ASX?
It’s typically on the radiator’s filler neck at the front of the engine bay, with the overflow bottle nearby. Some market or engine variants may place the pressure cap on a dedicated filler neck, always look for the warning label and never open it hot.

What pressure radiator cap does the 2018 ASX use?
Most petrol ASX models use a cap around 1.1 bar (108 kPa). Always confirm the rating stamped on your existing cap or in service information and replace like-for-like to maintain correct boiling point and system behaviour.

How often should the radiator cap be replaced?
Have it checked at each coolant service. If it fails a pressure test, shows perished seals, or is original after about five years/100,000 km, replace it. It’s a low-cost part that can prevent costly overheating dramas.