I currently work for Daimler Commercial Vehicles.
The Mercedes-Benz OM642 engine is a 3.0 litres, 24-valve, aluminium/aluminium block and heads diesel 72° V6 engine manufactured by the Mercedes-Benz division of Daimler AG.
It is a verry reliable engine, power output is 188-261 hp (140-195 kW)/3,600-4,000
Torque, lb ft 325-457 lb-ft (440-620 Nm)/1,600-2,400.
The first thing that starts to fail on this engine is the crankcase ventilation system. Driving mostly in the city and low-quality fuel contribute to the formation of a large amount of deposits inside the intake system. The crankcase ventilation system vents to the intake of the turbocharger. The vented oily air easily goes through the turbo blades and this oil and sludge begin to accumulate on walls of the intake channels, swirl valves and etc. Mercedes-Benz has stated that this engine feature is "normal". Therefore, for vehicles equipped with an OM642 3.0L diesel engines, it will be helpful to clean an air intake manifold, intake pipes, and crankcase ventilation pipes every 60-80k miles. Otherwise, the swirl valves may be stuck and an overloading electric drive motor will blow a fuse that controls other sensors. If it will happen, the vehicle enters the "limp home" mode and limits engine speed.
The next problem applies to engines manufactured before 2010. The pre-2010 OM642 engines often had oil leaks from the oil cooler. This issue happened due to heat-related seal degradation. In 2010, the manufacturer replaced the previous orange seals with more durable Viton seals. New seals have a purple color.
Injector copper seals are known to fail, causing a build up of heavy carbon deposits around the injector. The car begins to smoke and lose power. As a result, it all ends with the failure of the fuel injectors (known in the shop as "Black Death").
These engines are fitted to just about 98% of ambulances in Australia and they do a great job.
