Mercedes-Benz OM 138

The Mercedes-Benz OM 138 is a diesel engine manufactured by Daimler-Benz. In total, 5,719 units were produced between 1935 and 1940. It was the first diesel engine especially developed and made for a passenger car. The first vehicle powered by the OM 138 was the Mercedes-Benz W 138. The light Mercedes-Benz trucks L 1100 and L 1500 as well as the bus O 1500 were also offered with the OM 138 as an alternative to the standard Otto engine.

Impact

Daimler-Benz started mass production of the six-cylinder inline truck diesel engine OM 5 in 1928. Technical improvements allowed an increase in rated rotational speed, thus allowing more power with lower displacement, which made it possible to use the diesel engine as a car engine. Diesel engines have significantly lower running costs than Otto engines; this was the motivation for the adaption of the diesel engine as a car engine. The W 138 powered by the OM 138 has a fuel consumption of 10 L/100 km (28 mpg_‑imp; 24 mpg_‑US), whereas its Otto-powered counterpart W 21 has a fuel consumption of 13 L/100 km (22 mpg_‑imp; 18 mpg_‑US). Caused by the lower diesel fuel price compared to petrol, the W 138 was favoured especially by taxi drivers.

Even though the OM 138 was designed as a car engine, 3,752 out of 5,719 engines produced were used in trucks. The OM 138 marked the beginning of Daimler-Benz car diesel engine production; however, until Volkswagen AG introduced its EA 827 in the Golf I in the 1970s, the diesel engine was uncommon as a passenger car engine in Germany.