The long-standing belief that Japanese automotive manufacturing is synonymous with absolute reliability and unbreakable drivetrains suffers a serious blow when it comes to diesel engines. While companies from the Land of the Rising Sun dominate gasoline and hybrid technologies, their engineers have repeatedly made fundamental mistakes in the development of diesel units. Most of these units develop defects long before reaching the 200,000 kilometer mark, becoming a real nightmare on the secondary market.
Mazda 2.0 MZR-CD (RF7J)
Created with the idea of meeting strict environmental standards in Europe, this two-liter engine turns out to be too capricious. Its main drawback is the dilution of engine oil with diesel fuel, which begins after the first 120,000 kilometers. Repeated cleaning cycles of the particulate filter in urban environments, together with defective diphthongs under the nozzles, introduce fuel into the lubrication system. As a result of oil starvation, the camshafts, turbocharger and connecting rod bearings are destroyed. The loss of tightness of the intercooler and vacuum pump further shorten the life of the unit.
Subaru EE20 Z
Subaru's attempt to bring its boxer concept to diesels looked promising due to its low center of gravity and low fuel consumption. In real life, however, the complex architecture creates a lot of headaches. At a mileage of about 150,000 kilometers, accelerated wear of the connecting rod bearings is often observed, and a drop in oil pressure leads to engine blocking. The first series suffered from cracks in the crankshaft due to high torsional loads. What's more – the boxer layout makes even basic repairs extremely expensive, including replacing the timing chain.
Toyota 1AD-FTV
Toyota's aluminum unit debuted with the ambition of being modern and economical, but quickly showed its flaws. By 150,000 kilometers, many cars with this engine experience problems with the cylinder head gasket, causing overheating and deformation of the block itself. Although in later versions after the facelift the block was reinforced, high oil consumption remains chronic. Rapid contamination of the exhaust gas recirculation (EGR) valve and clogging of the particulate filter make urban operation a real test.
Nissan YD25DDTi
Known from legendary pickups and SUVs, this engine has great torque, but also carries serious congenital defects. The most serious among them is the tendency to burn out or burst pistons, registered in some modifications as early as 120,000 kilometers. The cooling system is highly sensitive to load, and overheating almost certainly leads to the departure of the piston group. Early stretching of the timing chain and high maintenance costs for the fuel system further aggravate the situation.
Mitsubishi 4N15
With this unit, Mitsubishi made a technological leap, introducing for the first time an aluminum block in its diesels, combined with a MIVEC variable valve timing system. However, the weight reduction came at the expense of durability. Aluminum is extremely difficult to handle overheating, and the first batches suffered from stretching the timing chain before 100,000 kilometers. The complex emission control peripherals make the engine demanding on fuel and oil, depriving it of the basic maintenance that the brand's older cast iron engines were known for.
Toyota 1KD-FTV
The three-micron diesel is a true legend among off-road enthusiasts, but its Euro 3 and Euro 4 versions hide a serious risk factor. Due to the high thermal stress on the piston heads, cracks form, accompanied by a loss of compression. The problem is exacerbated by the fuel injectors - when they start to leak, they locally overheat the piston. Burnt copper washers under the nozzles allow gases into the crankcase, which quickly turns the oil into resin and clogs the oil pump, leading to total damage.