Mercedes-Benz OM 138
| OM 138 | |
|---|---|
| Overview | |
| Manufacturer | Daimler-Benz AG |
| Production | 1935-1940 |
| Combustion chamber | |
| Configuration | Inline-4 |
| Displacement | 2545 cc |
| Cylinder bore | 90 mm |
| Piston stroke | 100 mm |
| Cylinder block alloy | Grey cast iron |
| Valvetrain | OHV |
| Compression ratio | 20,5:1 |
| Combustion | |
| Fuel system | Precombustion chamber injection |
| Fuel type | Diesel oil |
| Oil system | Wet sump |
| Cooling system | Water-cooled |
| Output | |
| Power output | 33 kW |
| Dimensions | |
| Dry weight | 300 kg |
| Chronology | |
| Predecessor | None |
| Successor | OM 636 |
The Mercedes-Benz OM 138 is a diesel engine manufactured by Daimler-Benz: 5,719 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 an otto engine.
Daimler-Benz started the mass production of the six-cylinder-inline-truck-diesel-engine OM 5 in 1928. Due to technical improvements, the rated rotational speed could be increased, which made it possible to use the diesel engine as a car engine. Diesel engines have siginifantly 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, while its otto-powered counterpart W 21 has a fuel consumption of 13 l / 100 km. 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 a car engine, 3.752 out of 5.719 engines produced were used as truck engines. With the OM 138, the Daimler-Benz car diesel engine production started, however, until the Volkswagen AG introduced its EA 287 in the Golf I, the diesel engine was uncommon as a car engine in Germany.
The development of a passenger car diesel engine began in the autumn of 1933. An inline-six-cylinder truck diesel engine with a displacement of 3,8 l was used. It produced 59 kW (80 PS). This engine however caused vibrations that were too strong for prototype car chassis, so that Daimler-Benz tried to develop a less powerful and smaller diesel engine. Two prototype engines were developed from scratch: The OM 134, a water-cooled inline-three-cylinder engine with a rated power of 22 kW (30 PS) and the OM 141, an inline-four-cylinder engine producing 26 kW (35 PS). These engines did not fulfill the requirements. Daimler-Benz decided to use the truck engine again to develop a fitting powerplant for a car. In 1934, the cylinder amount of the truck engine was reduced to four, bore and stroke were kept. Problems such as strong exhaust emissions and a rough engine running were solved, mass production could begin in 1935.
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