Mitsubishi Delica: 4M40 head gasket failure at high mileage

The 4M40 2.8 diesel is susceptible to head gasket failure on high-mileage examples, typically presenting above 200,000 km or after overheating events. The alloy head is prone to warping if the engine has ever run hot, and the factory head bolt torque specification leaves little margin once the gasket begins to compress with age. Head gasket failure allows combustion gases into the coolant, pressurising the cooling system and causing rapid coolant loss. It is one of the most commonly reported terminal failures on neglected L400 Delicas presented for roadworthy.

• White or grey smoke from the exhaust at idle and under load with a sweet smell
• Coolant loss with no visible external leak, cooling system pressurising rapidly
• Milky or emulsified residue on the oil filler cap or dipstick

1. 1

   Check oil filler cap underside for white mayonnaise-like emulsion.

2. 2

   Check the coolant reservoir for oily contamination or dark discolouration.

3. 3

   Use a block test (combustion gas test kit) on the coolant reservoir with the engine warm.

4. 4

   Check for white sweet-smelling exhaust smoke at idle.

5. 5

   If a workshop inspection is possible: Perform a cooling system pressure test and observe for rapid pressure rise from combustion gas ingress.

Parts involved: Head gasket.

≈A$1,660 to ≈A$3,680 at independent workshop rates, shown as an approximate guide in Australian dollars. That is for this job on its own, not for the car.

An estimate, converted to Australian dollars, 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 vehicle ever overheated, and if so how badly?”
• “What is the current mileage, and has the head gasket ever been replaced?”
• “Has the cooling system been pressure tested recently?”

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.