The M51 is a water-cooled and turbocharged inline six-cylinder diesel engine with a Bosch VP37-swirl-chamber-injection.

Some engine variants have an intercooler in addition to the turbocharger, they can be identified by the tds.

[2] The M51 is an engine made of cast iron, it has one chain driven overhead camshaft[4] and two valves per cylinder.

[2][4] Compared to the M21 the M51 now has tappets and a hydraulic valve lash adjustment.

[2] The fuel injection in the first engines and all E36 models is controlled by the ECU Bosch DDE 2.1, which was replaced after the first technical revision by the DDE 2.2[4] This results in greater torque at lower revs.