OM646

It arrived in 2002 in the W211 E 220 CDI as a reworking rather than a replacement, and the reworking was thorough. Bosch common rail at up to 1,600 bar, injectors spraying through seven holes, and — new here — a double pilot injection that warmed the chamber before the main event so the pressure rise was gentler and the clatter less. The variable-geometry turbo gained electronic vane control, the intake kept switchable swirl and tangential ports, the mechanical lift pump gave way to an electric one in the tank, and the 220 CDI versions ran a pair of Lanchester balance shafts.

From there it went nearly everywhere: C-Class, E-Class, CLK, CLC, Vito and Viano, the W906 Sprinter, and — as the OM644, turned sideways for front-wheel drive — the Chrysler PT Cruiser 2.2 CRD. The 2006 EVO revision altered ninety more parts, dropping compression to 17.5:1 on taller pistons and shorter rods, fitting ceramic glow plugs and giving every version balance shafts; it also absorbed the work of the five-cylinder OM647. Outputs ran from 88 to 170 PS before the OM651 took over in 2010.