Mechanics hail Mercedes diesel as one of the most durable ever, with cars surpassing one million kilometres

The Mercedes OM 617 became famous not for advanced technology, but for surviving almost everything around it. Mechanics have long regarded the five-cylinder diesel as capable of covering more than one million kilometres, a distance that is difficult to imagine for many modern cars.

The engine powered the well-known Mercedes W123 and helped turn that model into a favourite among taxi drivers around the world. Produced from 1974 to 1991, it belonged to an era when diesel engines typically delivered modest power for their size.

Its design relied on heavy pistons and connecting rods, a sturdy engine block and an oversized crankshaft. The engine used straightforward mechanics rather than complex electronics, meaning routine servicing, oil changes and repairs generally required an experienced mechanic and basic tools instead of advanced diagnostic equipment.

That longevity came with clear trade-offs. The 3.0-litre OM 617 fitted to later 300 D versions produced 88 horsepower, resulting in slow acceleration and a rough, almost tractor-like sound. For W123 enthusiasts, however, those shortcomings were acceptable. In some cases, the vehicle’s body deteriorated before the engine itself.