Mitsubishi Pajero Sport: 4M40 2.8 turbo diesel cracked cylinder head (linked to overheating and timing chain stretch)

The 4M40 2.8 turbo diesel is known for cracking its cylinder head, usually between the valves or near the exhaust ports. Causes cited by specialists are high exhaust temperatures from towing or over-fuelling, a neglected cooling system and thermostat, and stretch in the timing chain which retards the timing so combustion runs hotter in the exhaust side. The 4M40 has a chain rather than a belt, and some mechanics advise checking or replacing it at around 150,000 km. A cracked head pushes coolant out and gas into the cooling system and ends in overheating; the repair is a new or reconditioned head.

• Coolant level dropping with no visible leak
• Bubbles or surging in the coolant reservoir with the engine running
• Temperature gauge rising when towing or climbing
• White smoke or a sweet smell from the exhaust
• Rattle from the front of the engine on a cold start (stretched chain)

1. 1

   Ask for the engine to be completely cold when you arrive.

2. 2

   Look at the coolant reservoir level and colour before starting; brown sludge or oil in it is a bad sign.

3. 3

   Start the engine and watch the reservoir for bubbles or coolant being pushed up as it warms, and listen at the front of the engine for a chain rattle in the first few seconds.

4. 4

   On a test drive of at least 20 minutes including a hill, keep an eye on the temperature gauge, which should sit mid-scale and not climb.

5. 5

   Ask if it has towed a caravan or boat and whether the head, thermostat or timing chain has ever been done.

6. 6

   If a workshop inspection is possible: have a combustion gas (block) test done on the coolant and a cooling system pressure test.

Parts involved: Timing chain, Cylinder head, Turbocharger.

$3,500 to $7,500 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 cylinder head ever been replaced or repaired?”
• “Has the car been used for towing, and how heavy?”
• “Has the timing chain or thermostat ever been replaced?”
• “Does it ever need coolant topped up?”

The failure described above is documented in the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

• 4x4community.co.za forum thread 'Cracked Head on 2.8TDI' (4M40)
• 4x4community.co.za forum thread 'Timing Chain' (4M40 chain stretch and cracked heads, 150,000 km change advice)
• Grassroots Motorsports forum 'Calling Mitsubishi 4M40 experts' (cracked head reports)