Mitsubishi Pajero: 4D56 2.5L Diesel Head Gasket Failure and Head Bolt Stretch

The 4D56 engine has a well-documented history of head gasket failure, particularly at high mileage or following any overheating event. The head bolts are prone to stretching under repeated thermal cycling, allowing the gasket to weep coolant internally or externally. Mitsubishi issued revised head bolt specifications and updated gasket kits. A blown gasket on the 4D56 leads to coolant mixing with engine oil, white exhaust smoke, and if untreated, terminal engine damage from hydrolocking or oil dilution.

• White or grey smoke from exhaust particularly on start-up
• Coolant level dropping with no visible external leak
• Mayonnaise-like residue on oil dipstick or filler cap
• Engine overheating episodes
• Bubbling or gurgling in coolant expansion reservoir

1. 1

   Check the coolant reservoir for an oily film or bubbling when the engine is at operating temperature.

2. 2

   Use a combustion gas analyser (block tester) in the coolant reservoir to detect exhaust gases.

3. 3

   Inspect the exhaust for sustained white smoke distinct from cold condensation.

4. 4

   Remove the oil filler cap and dipstick and inspect for white mayonnaise emulsion.

Parts involved: Head gasket.

$1,800 to $4,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the head gasket ever been replaced?”
• “Has the engine ever overheated — even briefly?”
• “When was the coolant last flushed and were any leaks found?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.