Toyota Hilux 1KD-FTV EURO 4 Spec
Models – KUN26, KDJ120, KDJ125, KDJ150, KDJ155
Fault – Crack in piston, can lead to localised rupture
Symptoms – Sudden loss of power, engine runs rough (on 3 cylinders), loud knock at idle, black smoke from exhaust, excessive crankcase pressures
When disassembling the engine, there are cracks detected in one or more pistons (various sizes, up to a local ruptures). The look is radically different from the cases of usual piston melting, and only small local flowing can be observed in the areas of ruptures.
The 1KD engine has been sold in Australia for over 10 years, and has had a bumpy ride in terms of engine reliability. The first production of the engine is not affected by this issue as it featured a piston design which included a metal fibrous structure fused into the piston crown (as pictured). This structure added extra strength to the piston thus avoiding failure.
The engine underwent Euro 4 emissions modification which coincided with an overall modernization – reduced compression ratio, increased torque and power. The shape of the combustion chamber in the piston was changed, and any mention about the reinforced zone disappeared. Considering the circumstances of occurrence, the cause of the problem should be called “inadequate strength margin on pistons”, essentially it comes down to design and construction mistakes on the Euro 4 version of the engine.
Three years later the obviously substandard pistons were replaced by a new revision, however whilst this was an improvement, failures were still occurring, but at a lesser rate than previous. Contributing factors are also associated with the fuel system, but are secondary.
The failures are most commonly occurring around the 100,000 – 150,000 km. The problem is recognised by Toyota in several service bulletins released between 2011 and 2014.
Euro 5 revisions brought yet another design change, and whilst it’s still early days, it looks like the problem may have been resolved. Time will tell.
Owners and potential buyers of the “EURO 4” affected models of the Hilux, Prado and Hi-ace should be wary. The advice is simple, avoid chip tuning, avoid long driving at high speeds (especially under load) and service the fuel injectors every 100k. This will reduce the likelihood of failure, but the only to overcome the inherent design fault is to change the pistons. Speak to Southside Cylinder Heads today about repair and failure prevention options. Engines & cylinder heads since 1977.