Mercedes-Benz OM 138

The Mercedes-Benz OM 138 is a diesel engine built by Daimler-Benz, of which 5,719 units were produced between 1935 and 1940. It was the first diesel engine developed and made especially for a passenger car, and the first vehicle it powered was the Mercedes-Benz W 138. Development began in the autumn of 1933 under Albert Heess, who reworked a 3.8 litre six-cylinder truck diesel by cutting it to four cylinders after two smaller prototypes, the OM 134 and OM 141, failed to meet requirements. The result is a naturally aspirated, water-cooled inline-four with precombustion chamber injection. Of the units built, 3,752 went into trucks, and the W 138 used about 10 litres per 100 km against 13 for its petrol counterpart, which made it popular with taxi drivers.