Parts for your 1991 Mitsubishi Pajero-Radiator cap

1991 Mitsubishi Pajero Radiator Cap — What It Does and How to Look After It

Based on the Mitsubishi Pajero/Montero Factory Service Manual (Cooling System section, early 1990s editions), the Mitsubishi ASA electronic parts catalogue, and well-known aftermarket catalogues from Tridon and Gates, a pressure-type radiator cap is fitted to 1991 Mitsubishi Pajero models (including 4D56T diesel and 6G72 V6). So yes — a radiator cap is relevant and used on this vehicle.

On a 1991 Pajero, the radiator cap does more than just seal the filler neck. It regulates cooling-system pressure so coolant boils at a higher temperature, helping the wagon stay cool when towing, climbing, or crawling off-road. It also has a vacuum valve to pull coolant back from the overflow bottle as the system cools down, keeping air out and the system topped up.

Most 1991 Pajero variants run a cap stamped around 0.9 bar (13 psi), with some trims specified up to 1.1 bar (16 psi). The correct rating is printed on the cap and listed in factory data, using the proper pressure cap protects hoses, the radiator core, and the heater matrix.

As part of routine servicing, the cap’s worth checking or swapping every couple of years, especially if the 4WD sees heavy work or lots of heat cycles. A weak spring or perished seals can cause overheating, coolant loss, rough idle from air pockets, or a collapsed upper hose after cool-down.

• Inspect when cold: look for cracked or flattened rubber seals, a sticky centre valve, corrosion or crust around the seat, and damaged tabs.
• Pressure test: a simple cap tester will confirm it holds the rated pressure and releases cleanly.
• Clean the neck: wipe the filler neck seat so the new cap seals perfectly.
• Replace on schedule: typically every 2–4 years or 40–60,000 km, sooner if symptoms show.

When removing, only open the cap stone-cold. If it must be opened warm, use gloves and turn to the first stop to bleed pressure before lifting off. Match the cap style to the Pajero’s Japanese-style neck and the specified pressure rating. Pairing a fresh cap with correct coolant mix and good hoses is cheap insurance for a long-lived 6G72 or 4D56T under the bonnet.

• Signs it’s time: rising temps under load, coolant smell after shutdown, overflow bottle filling but radiator low, or hoses going flat after cooling.

Popular questions about 1991 Mitsubishi Pajero radiator caps

What pressure radiator cap does a 1991 Pajero use?
The factory information and parts catalogues typically show 0.9 bar (13 psi), with some trims at 1.1 bar (16 psi). It’s best to match what’s stamped on the original cap or check the service manual for the exact engine and market.

Where is the radiator cap on a 1991 Pajero?
It’s on the radiator’s top tank under the bonnet, with a separate overflow bottle nearby. The cap locks onto the radiator filler neck with two tabs.

How often should the radiator cap be replaced?
For Aussie and Kiwi conditions, every 2–4 years or 40–60,000 km is a safe bet, or immediately if testing shows it won’t hold the rated pressure, the seals are perished, or there are overheating symptoms.