Parts for your 1988 Mitsubishi Pajero-Radiator cap

1988 Mitsubishi Pajero radiator cap — what it does and when to replace it

Technical sources confirm a radiator cap is fitted and relevant on the 1988 Mitsubishi Pajero. The Mitsubishi Pajero/Montero Factory Service Manual (1988, Cooling System section) specifies inspection and pressure ratings for the cap on first‑gen models. Gregory’s/Haynes Mitsubishi Pajero 1983–1996 repair manuals also show cap testing and replacement on both petrol and diesel variants. Mitsubishi’s ASA electronic parts catalogue lists a “CAP, RADIATOR” for 1988 Pajero applications, with location either on the radiator neck or, on some variants, a pressurised surge tank.

On a classic ’88 Pajero, the radiator cap quietly does a lot of heavy lifting. It seals the cooling system and holds a set pressure so coolant can run hotter without boiling, which helps keep temps stable climbing long hills or towing the boat. Inside the cap is a spring-loaded pressure valve and a little vacuum valve. When things heat up, the pressure valve lets expanding coolant move to the overflow bottle. As it cools, the vacuum valve draws coolant back in so the system stays full and air-free under the bonnet.

Because that small part controls pressure, a tired cap can cause annoying symptoms: coolant loss, collapsed hoses after shutdown, or overheating at highway speeds. It’s worth checking the cap any time the coolant’s serviced. A quick look for cracked rubber seals, a sticky centre plunger, or crusty deposits is a good start. Better yet, pressure-test it to the rating stamped on the cap and confirm it holds steady.

• Choose the correct pressure rating for your engine and market (commonly around 0.9–1.1 bar, match the old cap’s stamping or the FSM).
• Inspect the radiator neck or surge tank seat for nicks and corrosion so the new cap can seal properly.
• Replace the cap every few years, or whenever you do a coolant refresh, to stay ahead of age-related failures.

When swapping it out, make sure the engine is stone cold. Use a rag, press down, and turn the old cap off carefully. Fit the new one squarely and tighten by hand until it seats with a firm twist. After a few drives, check for any signs of seepage around the neck and confirm the overflow hose is snug. It’s a small, cheap bit of kit that can save the Pajero from bigger cooling headaches across Aussie and Kiwi kilometres.

Popular questions about the 1988 Mitsubishi Pajero radiator cap

What pressure rating does the 1988 Pajero radiator cap use?
It varies by engine and market, but many first‑gen Pajeros run a cap in the 0.9–1.1 bar range. The correct spec is stamped on the top of the original cap and listed in the Factory Service Manual. Matching that rating is important—too low and you’ll lose coolant early, too high and you can stress hoses and the radiator.

Where is the radiator cap on a 1988 Pajero?
Most Australasian 1988 Pajeros have the cap on the radiator’s top tank, front and centre under the bonnet. Some variants use a pressurised surge tank mounted off to one side—on those, the cap lives on the tank instead of the radiator neck.

Can a weak radiator cap cause overheating or coolant loss?
Yes. A weak spring or damaged seal lets pressure bleed off, dropping the boiling point and pushing coolant into the overflow too early. You might see overflow bottle surges, collapsed upper hoses after cooldown, or gradual overheating at speed. Testing or replacing the cap often resolves these issues quickly.