The Mercedes-Benz OM648 engine is a 3.2 Litre, straight-6 4 valves per cylinder, cast iron block diesel engine manufactured by the Mercedes-Benz division of Daimler AG as a replacement for the previous Mercedes-Benz inline-5 and -6 engines.

The engine features common rail fuel injection and a variable nozzle turbocharger.

The injection system operates at 1,600 bar (23,000 psi).

Mercedes claims this engine will propel the E320 CDI to 60 mph (97 km/h) in 6.6 seconds.

All while managing 27 mpg‑US (8.7 L/100 km; 32 mpg‑imp)+ city and 37 mpg‑US (6.4 L/100 km; 44 mpg‑imp)+ Highway[citation needed] Oil specification MB 229.31 or MB 228.31 is recommended and has a service interval of 13,000 miles (21,000 km) using the specified oil.