Nissan Pathfinder: YD25DDTi Head Gasket Failure

The YD25DDTi cylinder head gasket is a documented weakness, particularly on higher-mileage examples and vehicles that have experienced even a single overheating event. The failure is frequently preceded by or co-occurs with EGR cooler cracking, as the resulting coolant loss causes the engine to run hot. The aluminium cylinder head distorts at elevated temperatures, compromising the gasket seal between the combustion chamber and coolant passages. Combustion gases enter the cooling system, coolant enters the oil, and in severe cases coolant is drawn directly into the cylinder and burned. Engine damage escalates rapidly once the gasket has failed.

• Creamy or mayonnaise-coloured emulsion visible on the oil dipstick or under the oil filler cap, indicating coolant mixing with engine oil
• Coolant reservoir bubbling or pressurising rapidly when the engine is at temperature, caused by combustion gases entering the cooling circuit
• Persistent white exhaust smoke with a sweet odour and unexplained coolant consumption

1. 1

   Use a combustion gas (CO2) leak-detection fluid test on the coolant reservoir filler neck.

2. 2

   Check coolant colour for oily contamination.

3. 3

   Inspect the exhaust for white smoke and sweet odour.

4. 4

   Ask for any history of overheating, coolant warning lights, or EGR cooler replacement.

5. 5

   Remove the oil filler cap and dipstick — mayonnaise-like emulsion on either indicates coolant in the oil.

6. 6

   If a workshop inspection is possible: Pressure-test the cooling system; bubbling in the coolant reservoir while the engine runs points to combustion gas ingestion.

Parts involved: Head gasket.

$2,800 to $5,500 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? Is there a workshop invoice?”
• “Has the car ever overheated or had the temperature warning light activate?”
• “Has the EGR cooler been replaced — and if so, was the cooling system thoroughly bled and inspected at that time?”

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.