Parts for your 2018 Mitsubishi Eclipse cross-Radiator cap

2018 Mitsubishi Eclipse Cross radiator cap: what’s fitted and what to service

Based on Mitsubishi’s technical documentation for the GK-series Eclipse Cross (Cooling System section of the Mitsubishi Motors Service Manual) and the Mitsubishi ASA electronic parts catalogue for GK1W/GK2W, this model does not use a traditional radiator-mounted cap. The radiator is a sealed unit without a filler neck. System pressure and filling are handled by a pressurised expansion/degas tank, which has the only pressure cap in the system. Workshop procedures in the manual refer to removing the “reserve/expansion tank cap” for coolant service, not a radiator cap.

Why’s there no cap on the radiator? Modern cooling layouts place a pressurised expansion tank at the highest point in the engine bay. That setup lets air separate out more effectively, makes bleeding easier, supports tighter packaging under the bonnet, and suits plastic top-tank radiators that aren’t designed for a cap and filler neck. On the 2018 Eclipse Cross (including the 1.5T), the pressure cap lives on that expansion tank, functionally it’s the system’s “radiator cap”, just not on the radiator itself.

What should owners service instead? Treat the expansion tank pressure cap as the key item. It controls system pressure, raises the boiling point of the coolant, and allows coolant recovery as the engine heats and cools. If the cap’s spring weakens or the seals harden, you can get overheating, coolant loss, or hoses collapsing after cool-down.

• Inspect the cap at regular services for perished rubber, damaged seal faces, corrosion, or weak spring action.
• Only remove the cap when the engine is stone cold. Under pressure, hot coolant can spray out.
• Use a quality replacement with the correct pressure rating for your vehicle. The rating is stamped on the cap, Mitsubishi applications are commonly around 0.9–1.1 bar. Match what’s printed on your existing cap or specified in the service manual.
• Top up and bleed via the expansion tank, not the radiator. Use Mitsubishi-approved long-life coolant (blue) premix, and run the heater on hot during bleeding to circulate coolant through the heater core.

If you’re searching for a “radiator cap” for a 2018 Eclipse Cross, you’re really after the expansion/degas tank pressure cap. Replacing a tired cap is cheap insurance for stable temps on long Kiwi and Aussie drives.

FAQs

Does the 2018 Eclipse Cross have a radiator cap?
It doesn’t have a cap on the radiator itself. The cooling system uses a sealed radiator and a pressurised expansion tank. The pressure cap is fitted to that tank and does the same job a traditional radiator cap would.

Where do you add coolant on a 2018 Eclipse Cross?
Under the bonnet, fill and top up via the pressurised expansion/degas tank. Do it only when the engine is cold, use the correct long-life coolant premix, and bleed the system with the heater on hot. Recheck the level after a short drive once it’s cooled again.

What pressure cap does it use, and when should it be replaced?
Use a cap with the same pressure rating shown on your existing cap (commonly around 0.9–1.1 bar for Mitsubishi). Have it inspected at routine services, replace if the seals are cracked, there’s staining around the neck, hoses collapse after cool-down, or as preventative maintenance at high kilometres/years.