YD25 engine problems: timing chains, EGR coolers and when to replace

What goes wrong with the YD25?

The YD25 is the 2.5 litre turbo diesel in the D22 Navara from 2008, the D40 Navara and the R51 Pathfinder. Two problems come up most in the sources we checked: the timing chain and the EGR cooler.

Why does the YD25 timing chain fail?

The YD25 uses two chains: a double-row chain at the top and a single-row chain at the bottom. The single-row chain can stretch, and its guides and the vacuum pump sprocket can wear. If it stretches far enough, the timing slips and the valves can hit the pistons.

CarsGuide calls chain rattle a regular complaint on the D40, sometimes from about 50,000 km. One independent reference suggests renewing the chain and tensioners before 80,000 km and checking every 40,000 km after that. That is the reference's advice, not a Nissan schedule.

The sign is a rattle from the front of the engine. Don't ignore it. A chain that is only rattling is a repair; one that has jumped is usually an engine.

What is the EGR cooler problem?

The EGR cooler uses engine coolant to cool exhaust gas. It can corrode or split inside, or at its ends, and leak coolant into the exhaust. Because the coolant boils off, there is often no puddle, only a falling coolant level and staining around the EGR pipes. Left alone, the leak can overheat the engine and damage the head gasket. Taking the EGR off is not a legal fix.

What else is reported?

• Exhaust temperature sensors. Nissan ran a service campaign in 2013 to replace these sensors on 2012 and 2013 D40 and R51 diesels. A failed sensor can put the engine in limp mode at about 2,000 rpm.

When is a new YD25 the answer?

When the chain has jumped and the valves have hit the pistons, or when overheating has damaged the head and bottom end. Your mechanic can measure how far the damage goes with compression and leak-down readings and a check of the coolant for exhaust gas. See engine tests before replacing an engine.

What should be fixed before a new YD25 goes in?

• The EGR cooler: test it, and replace it if there is any doubt.
• The cooling system: radiator, hoses, thermostat, water pump and coolant.
• The turbo and its oil lines.
• The injectors, which come across from your old engine.

Damage from overheating or from a part we did not supply is not covered by the engine warranty. See fitting a new engine.

What YD25 engine does Reco list?

A new YD25 long bare motor with the AMC cylinder head, Euro 3, for the Navara D22 and D40 and the Pathfinder R51, listed at $6,950 on 15 October 2026. See what to check before buying a YD25 and the YD25 engine page.

Ask us about your YD25

Use the enquiry form with the vehicle's model, year, series, rego and VIN, and what happened. Or call 02 9737 0105.