OM629

The bones were the OM628's: a sand-cast aluminum bedplate crankcase split at crankshaft height, wet cast-iron liners, ductile-iron main bearings, the same square 86 × 86 mm cylinder, and the same awkward 75° vee with its balance shaft and split crankpins. What changed was the breathing and the burn. Compression came down to 17:1, the common-rail system was reworked, and each bank got a variable-geometry turbocharger feeding an air-to-water charge cooler with its own low-temperature circuit. The result was 306 to 320 PS at 3,600 rpm and up to 730 N·m.

It reached the road in 2005 in the W211 E 420 CDI, then the W221 S 420 CDI, and served longest in the heavy SUVs — ML and GL 420 CDI, rebadged 450 CDI from 2009 without changing the displacement. Then the format ended. When the last of them was built, Mercedes did not replace the diesel eight with another diesel eight: the flagship oil-burner job passed to the OM656, a straight six, and the V8 diesel remains something the company tried for two engine generations and then let go.