The history of the automotive world is not only marked by legendary car models; there is also room for engines that have made a name for themselves thanks to their excellent performance. There are many that would qualify for the pantheon of engines, but today we want to focus on the OM617 engine, a creation by Mercedes that marked a turning point for diesel engines in its day.
The German brand wanted to create a diesel engine that would stand out from the rest, and it certainly succeeded, coming up with an engine that is widely recognised as one of the most robust and reliable diesel engines ever built.
To talk about its beginnings, we have to look even further back than its creation. Its origin lies in another engine, the OM621, a 1.9-litre inline four-cylinder block that Mercedes-Benz developed in the 1950s, with a modest output of 50 hp, which was not bad for that time.
It was used in several models of the brand until it was used as the basis for developing the OM616, which in turn was the basis for creating the protagonist of our story: by adding an additional cylinder to make five, the OM617 was created, which began production in 1974 and had a very long career, as it was marketed until 1991.
The reason for its creation was that, without sacrificing the fuel economy of the 616 or compromising its reliability, it was necessary to create a more powerful engine. To achieve this, a fifth cylinder was added, the displacement of the block was increased to 3.0 litres and a overhead valve configuration with chain-driven camshafts was adopted.
Initially, it was a naturally aspirated engine, but over time it evolved to incorporate turbocharged versions, a key change that substantially improved its performance without compromising reliability.
Among the most notable versions of the OM617 are the OM617.910 / .912, both naturally aspirated and used mainly in the 300D and 300CD; and the OM617.950 / .951 / .952, already turbocharged and which formed one of the most beneficial partnerships in the entire history of Mercedes when combined with the equally legendary W123.
The OM617 is considered one of the most reliable engines in history, and this is not arbitrary. Over the years, numerous cars equipped with this engine have managed to break the million-kilometre barrier, which is no easy feat. But how did this engine achieve such high levels of quality?
The main thing is that, as Mercedes wanted its engine to last as long as possible, it spared no expense and built it using high-quality materials. The block is made of cast iron, while the cylinder head is made of aluminium alloy. This makes it easy to maintain and extremely resistant to wear and high temperatures.
In addition, it also benefits from an oversized construction, meaning that its components were designed to withstand more stress than they would normally experience during operation, so that under standard use they were not affected by wear and tear, as they could withstand much more.
Finally, it featured pressure lubrication, indirect injection and a glow plug preheating system (which was replaced in 1980 with a more reliable system).
When it was launched, its power output was only 80 hp, but subsequent improvements increased its performance. In 1978, the pre-combustion chamber was updated and in September it received a new camshaft. The result was an increase in power to 88 hp.
At the same time, turbocharged versions were developed. In 1976, the engine was adapted to use a turbocharger, allowing a considerable increase in power, which reached 110 and 125 hp in the road models.
Not only that, but a 190 hp version was installed in the IID version of the C111 test vehicle and, at the Nardó circuit in Italy, set 16 world speed and endurance records. Two years later, in 1978, it was revamped again to reach 230 hp and, mounted on the evolution of the test vehicle (now the C111-IIID), it set another nine additional records.
The OM617 was an extremely versatile engine, but it has made a name for itself for its durability and reliability, to such an extent that today, more than 40 years after it went out of production, there are still many cars with this engine on the road.
