1974-1976 Mercedes-Benz 240 D 3.0

40 years ago: The 240 D 3.0 was the first series-production car with a five-cylinder engine

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Stuttgart. – 59 kW (80 hp) signified a quantum leap in 1974: The five-cylinder diesel engine on board the Mercedes-Benz 240 D 3.0 produced such an output, making the model series 115, commonly known as the “Stroke/8”, the torquiest and fastest diesel-powered passenger car in the world. The diesel engine combined strong driving power with impressive economy. At the same time, the 240 D 3.0 was the first series-production car with a five-cylinder engine.

Five-cylinder diesel engines were not a totally new phenomenon 40 years ago - they had already proven successful in trucks and as stationary devices. Their use in a passenger car placed Mercedes-Benz in the headlines and assured the company of a pioneering role in the field of engine technology, however. The new engine accelerated the 240 D 3.0 from 0 to 100 km/h in 19.9 seconds, with a top speed of 148 km/h (automatic: 20.8 seconds, 143 km/h). This performance made the 240 D 3.0 the undisputed leader in the field of diesel-powered cars at the time of its press launch. “With its refined character, smooth running and economy (10.8 litres of diesel per 100 kilometres), the latest diesel-powered vehicle from Mercedes will appeal to a new and broad range of customers,” predicted the press announcement, claiming: “With the 240 D 3.0, driving a diesel has become even more attractive.” From a present-day perspective, the car undoubtedly paved the way for the continuing success of the company’s diesel cars.

One more cylinder for added output

Mercedes-Benz developed the OM 617 engine in response to the fact that the four-cylinder diesel engines used in passenger cars to date had reached their limits in terms of output. The need for more cubic capacity from which to coax more hp came up against the limited space available in the engine compartment. Tests conducted by Mercedes-Benz with a six-cylinder engine revealed it to be too long, too heavy, and too expensive. Five cylinders appeared to represent the ideal compromise.

The engineers developed the five-cylinder in-line engine OM 617 for use in series-production cars on the basis of a 2.4-litre OM 616 engine. The latter’s proven characteristics were retained, but the five-cylinder engine was provided with a new Bosch injection pump which was connected via oil ducts to the engine’s oil circuit and was thus maintenance-free. A mechanical governor replaced the pneumatic governor which was customary for the smaller diesel engines. This benefited driving comfort – the 240 D 3.0 with manual transmission revealed virtually no load alteration effects, and with automatic transmission gear-changing was substantially smoother in the partial load range.

The five-cylinder in-line engine’s increased cubic capacity of 3,005 cc produced an output of 59 kW (80 hp) at 2,400 rpm. The press reporters also welcomed the additional output: “This added power provides a very pleasant boost in practice. [...] To put it bluntly: The 240 D 3.0 is the first diesel car that can keep the pace in fast traffic without hindering other vehicles,” wrote “Auto Zeitung”. And “auto motor und sport” commented: “Despite the higher gearing, the 15 hp more in comparison to the 240 D provide the 3.0 with a pace that will also be to the liking of drivers who are not sworn diesel fans.”