Parts for your 1998 Mitsubishi Pajero-Radiator cap

1998 Mitsubishi Pajero Radiator Cap

Based on Mitsubishi Motors’ Factory Service Manual for Pajero/Montero (1997–1999, Cooling System section), the Mitsubishi ASA parts catalogue, and AU/NZ application guides from Tridon and Gates, the 1998 Mitsubishi Pajero is fitted with a pressure-type radiator cap. On most 4M40 2.8 diesel and 6G74 3.5 petrol models of this year, the cap sits on the radiator filler neck, with a specified opening pressure commonly around 0.9 bar (90 kPa), matched to the vehicle’s cooling system design.

The radiator cap on a 1998 Pajero does much more than just seal the top of the radiator. It regulates system pressure so coolant can run hotter without boiling, helping the engine keep its cool when towing, crawling in low-range, or sitting in summer traffic. It also controls the movement of coolant to and from the overflow bottle: the pressure valve lets expanding coolant vent to the reservoir, while the vacuum valve draws coolant back in as things cool down. That closed-loop action minimises air ingress and keeps the system topped up properly.

For servicing, it’s a small, inexpensive part that can cause big headaches if neglected. A tired cap can lead to hard hoses when hot, collapsed upper hose when cold, slow warm-up, or random overheating and coolant loss. As part of routine maintenance, it’s smart to:

• Inspect the rubber seals for nicks, flattening, or swelling, and check the spring feels firm.
• Pressure-test the cap to the Pajero spec (typically ~90 kPa) using a cap tester.
• Replace the cap every few years or at the first sign of doubt, especially if the cooling system’s been opened or the vehicle tows or works hard.

When replacing, match the pressure rating and neck type to the Pajero’s radiator. Stick with a quality OE-equivalent cap, the wrong rating can push coolant past the reservoir or, worse, stress the radiator and heater core. Only remove the cap when the engine is stone cold—use a rag, and crack it to the first notch to bleed off any residual pressure before removing fully. After fitting the new cap, confirm the overflow hose is snug, the bottle is filled to the “COLD” mark with the correct coolant, and take a short drive, then recheck levels under the bonnet once the engine cools.

FAQs

What pressure rating radiator cap does a 1998 Pajero use?
Most 1998 Pajeros use a cap around 0.9 bar (90 kPa). Always confirm against the under‑bonnet label, the Mitsubishi service manual for your engine code, or a reputable AU/NZ parts catalogue. Matching the factory rating ensures the cooling system holds pressure without over-stressing hoses or the radiator.

What are the signs the radiator cap is failing on a 1998 Pajero?
Common giveaways include random overheating, coolant pushing out into the overflow bottle and not returning, collapsed upper hose when cold, discoloured or crusty seal faces, and a cap that opens too easily. A quick pressure test will tell you if it’s holding the correct kPa.

Can a universal cap be used, or does it have to be Pajero-specific?
A universal cap can work if it exactly matches the pressure rating and neck depth/type used on the Pajero. However, an OE-equivalent cap from a trusted brand is the safer bet. The wrong cap can mask cooling issues or create new ones, especially when towing or working the vehicle hard.