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Meet the legendary Mercedes-Benz OM621 and OM617 engines: renowned for decades for their durability, these engines stand out for their reputation as being “unbreakable.” With an impressive capacity to run up to 1 million kilometers without needing overhauls.
In the late 50s, the German company Mercedes-Benz launched the OM621 engine, which was a 1.9-liter in-line four-cylinder engine that developed 50 horsepower and established itself as a family of durable engines on the market. The engine was used not only in the Unimog utility vehicle but was also used in passenger cars, equipping the W121 and W110 series.. In the 70s, the OM617 variant was created with an extra cylinder, increasing the volume to 3 liters and the power to 80 horsepower. In this article, we will learn all about these Mercedes-Benz engines that made history.
Mercedes-Benz engines gain a reputation for durability
In the late 70s, the company created a turbocharged version with up to 125 horsepower that equipped the famous 300 TD. The OM621 and OM617 engine family had indirect injection and was equipped with a Bosch in-line pump and injector, and the overhead valve control was chain-driven.
This family of durable engines has gained an excellent reputation, being considered robust, economical and reliable, whose durability is legendary, with reports of cars that have traveled over 1 million kilometers without needing overhaul and even some cases that have managed to exceed two million.
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The first naturally aspirated version of Mercedes-Benz engines was offered with the W115 240D 3.0 which flanked the 240-cylinder 4D: it had a displacement of 3.005 cm³ and delivered a maximum power of 79 horsepower.
To improve combustion distance and comply with new tax laws in Europe, in August 1978 Mercedes-Benz engineers updated the OM617 engine, fitting it with a new pre-combustion chamber and slightly reducing the bore to 90,9 mm for a displacement of 2.998 cc.
OM621 and OM617 engine families receive updates
Exactly one year later, the durable OM617 engines underwent mechanical refinement when they introduced a new camshaft that allowed greater lift of the intake and exhaust valves.
Power therefore increased to 88 horsepower, while torque remained unchanged at 17,5 kgfm. In this version, the engine equipped the W123, ancestor of the E-Class, the TN series vans and the W460 and 461 off-roaders of the G-Class, which were also the last to offer it until 1991.
It is worth mentioning that in 1976 a turbocharged variant signed OM617A, which developed the beauty of 187 hp, equipped the C111-IID prototype, setting several speed and duration records on the Nardò test circuit.
It was necessary to wait until 1978 for the arrival of the Mercedes-Benz 5-cylinder turbo engine on the market: that year in the North American market – the S-Class W116 was offered in the 300SD variant which made it the first turbodiesel sedan in the world.
The power of the OM621 and OM617 engines was reduced to 109 hp with 23,2 kgfm of torque later increased to 119 hp and 24,5 kgfm and then again to 125 hp and 25,5 kgfm and also used in several versions of the W123.
Why were Mercedes-Benz engines more durable?
Newer engines, despite undergoing various tests, still need time to mature. This means that, even after all the tests carried out by the manufacturers, a problem can always arise when the car hits the streets.
That’s why, when it comes to durable engines, the experience of the oldest and most robust ones still holds great value. They have already undergone years of use, improvements and adjustments, becoming an extremely reliable option for those looking for a car that will last.
