Parts for your 2003 Mitsubishi Pajero-Radiator cap

2003 Mitsubishi Pajero radiator cap — what it does and when to replace it

Technical references confirm the 2003 Mitsubishi Pajero is fitted with a radiator cap. The Mitsubishi Motors Workshop Manual for NM/NP series (Group 14: Cooling) specifies radiator-cap inspection and pressure testing as part of routine service, and the Mitsubishi ASA parts catalogue lists a dedicated cap for 2000–2006 Pajero/Montero models across common engines (including 3.2 Di‑D and 3.5/3.8 V6). Reputable aftermarket catalogues used in Australia and New Zealand (e.g., Tridon, Gates/Dayco) also specify a direct-fit pressurised radiator cap for these vehicles.

On a 2003 Pajero, the radiator cap is a small but critical bit of kit. It seals the cooling system and holds a set pressure so coolant can run hotter without boiling, which keeps the engine comfy under the bonnet on long hauls and slow, steep climbs. The cap’s spring-loaded valve maintains system pressure (typically around 0.9–1.1 bar for Pajero of this era — check the stamping on the cap for the exact rating), while a second valve lets coolant flow back in from the overflow bottle as things cool down. If that pressure control goes out the window, you can cop overheating, coolant loss, or hoses that collapse as the engine cools.

As part of regular servicing, the radiator cap deserves a once-over. Under a cold engine only, check the rubber seals for cracks or flattening, and look for corrosion on the seat and underside. If the spring feels weak or the cap looks tired, it’s cheap insurance to replace it. A cooling system pressure tester with a cap adaptor is the proper way to confirm health — the cap should hold its rated pressure without a drop for at least a minute. Always refit a cap with the correct pressure rating for the specific engine and VIN, using a higher or lower rating than spec can stress the radiator, heater core, and hoses.

• Replace the cap every 2–3 years or 40,000–60,000 km, or sooner if any faults show.
• Only remove the cap when stone-cold. Use a rag and turn to the first stop to vent, then fully off.
• If you’re chasing minor overheating, unexplained coolant loss, or a hard upper hose when cold, start with the cap test.

Done right, a fresh, correct-spec radiator cap helps the Pajero stay cool towing the boat, crawling in low range, or clocking big kilometres across the Nullarbor.

Popular questions about 2003 Mitsubishi Pajero radiator caps

What pressure radiator cap does a 2003 Pajero use?
Most 2003 Pajero engines specify a cap around 0.9–1.1 bar (roughly 13–16 psi). The exact rating is stamped on the cap and listed in the vehicle’s service data. Matching the factory rating is important to protect the radiator and heater core while keeping the boiling point high enough under load.

Where is the radiator cap on a 2003 Pajero?
It’s typically on the radiator neck under the bonnet, with a separate non‑pressurised overflow bottle nearby. Look at the top tank of the radiator, the cap will be the metal, bayonet-style fitting. Only open it when the engine is fully cold.

How often should the radiator cap be replaced?
As a rule of thumb, every 2–3 years or 40,000–60,000 km, or any time it fails a pressure test or shows perished seals or corrosion. Given the low cost and high stakes, many workshops fit a new cap whenever they service or flush the cooling system.