Parts for your 1999 Mitsubishi Pajero-Radiator cap

1999 Mitsubishi Pajero Radiator Cap: Purpose, Care and When to Replace

Technical sources confirm the 1999 Mitsubishi Pajero does use a conventional radiator cap on the radiator filler neck, it’s not a cap‑less, remote pressurised tank system. The Mitsubishi Pajero/Montero Workshop Manual (1997–2000, Cooling System section) illustrates the cap and overflow bottle layout, the Mitsubishi ASA electronic parts catalogue lists a serviceable radiator cap for 1999 Pajero variants, and common aftermarket catalogues (e.g., Gates/Stant) specify a direct‑fit pressure cap for these models. Haynes service manuals for 1991–1999 Pajero/Montero also describe cap inspection and testing.

On this Pajero, the radiator cap does more than just seal the top—it's a pressure regulator and a two‑way valve. By holding around 0.9 bar (roughly 90–110 kPa, ~13 psi), it lifts the coolant’s boiling point, helping the V6 petrols and 2.8 diesel keep their cool under load. When pressure rises, the cap lets excess coolant move to the overflow bottle, as the system cools, it draws coolant back, keeping the radiator brimmed and air out.

Owners should treat the radiator cap as a service item. Check it at every service or at least annually. Look for perished rubber seals, a weak or sticky spring, corrosion, or white crust around the filler neck. A cap that no longer holds pressure can cause hot‑day overheating, coolant loss into the bottle without return, or collapsed hoses after cool‑down. If there’s any doubt, pressure‑test it to its rated kPa with a cap tester—most workshops have one.

Replacement is simple and inexpensive. Choose the correct pressure rating and neck style for the specific engine/VIN. Only remove the cap when the engine is stone cold, wrap a rag around it and crack it slowly to release any residual pressure under the bonnet. Clean the filler neck, fit the new cap firmly, and make sure the overflow hose is clear and tight. After any cooling system work, run the engine with the heater on, top up with the correct premix coolant that meets Mitsubishi specifications, and check for air bubbles and stable level in the overflow bottle.

• Typical symptoms of a failing cap: coolant smell, dampness around the cap, frequent top‑ups, overheating at low speed, or hoses that flatten after a cold start.
• Practical tip: replace the cap whenever doing a major coolant service (every 2–5 years) to keep pressure control spot on.

Popular questions about 1999 Mitsubishi Pajero radiator caps

What pressure cap does a 1999 Pajero use?
Most 1999 Pajero variants run a cap around 0.9 bar (about 90–110 kPa, ~13 psi). Always match the rating stamped on the original cap or confirm by VIN/engine in a parts catalogue or workshop manual, as some engines and markets vary.

Can it be driven with a faulty radiator cap?
It’ll likely drive, but it’s risky. A weak or stuck cap can cause coolant loss, boil‑over, or air ingestion, which leads to overheating and possible engine damage. Replace or test the cap before a long trip or towing.

How often should the radiator cap be replaced?
Inspect at every service and pressure‑test yearly. Many owners replace the cap every 3–5 years, or immediately if it fails a pressure test, shows cracked seals, rust, or persistent coolant staining at the neck.