Mercedes-Benz OM621 engine
# Mercedes-Benz OM621 engine

The OM621 is an inline-four diesel engine produced by Mercedes-Benz, from 1956 to 1968. It was succeeded by the OM615 engine.

## Design

The OM621 is based on the petrol M121 engine, but features revised camshafts, cylinder head, pistons, and fuel injection system. In 1961, the engine capacity was increased to 2.0 L (1,988 cc) and power was uprated to 55 PS (40 kW) for use in the newly introduced W110 models. After being replaced by the OM615, a 2.2 L (2,197 cc) updated version of the OM621 engine was used solely in Unimog vehicles until 1988.

## Models

| Engine | Displacement | Power | Torque | Years |
| - | - | - | - | - |
| OM621 I | 1.9 L (1,897 cc) | 37 kW (50 PS) at 4,000 rpm | 108 N⋅m (80 lb⋅ft) at 2,200 rpm | 1958–1959 |
| OM621 IV | 2.0 L (1,988 cc) | 35 kW (48 PS) at 3,800 rpm | 108 N⋅m (80 lb⋅ft) at 2,200 rpm | 1961–1962 |
| OM621 III / VIII | 2.0 L (1,988 cc) | 40 kW (55 PS) at 4,200 rpm | 118 N⋅m (87 lb⋅ft) at 2,400 rpm | 1961–1968 |
| OM621 III / VIII | 2.2 L (2,197 cc) | 40 kW (55 PS) at 3,000 rpm | 118 N⋅m (87 lb⋅ft) at 2,400 rpm | 1966–1988 |

### OM621 (37 kW version)

* 1958–1959 W121 190D, 190Db

### OM621 (35 kW version)

* 1961–1962 W120 180Dc

### OM621 (40 kW version)

* 1961–1965 W110 190Dc
* 1965–1968 W110 200D
* 1966–1988 Unimog 421
