OM621

It was not designed as a diesel at all. Stuttgart took the M121 petrol four of the 190 saloon and gave it new camshafts, a new head, new pistons and injection equipment, producing its first passenger-car diesel with an overhead camshaft in place of the OM636's pushrods. The 190 D of August 1958 made 50 PS at 4,000 rpm — modest, but enough that a diesel Mercedes no longer had to be bought purely on running costs. Buyers agreed: 20,629 in eleven months, then 61,309 of the 190 Db that followed.

In January 1959 Karl Kling, by then the company's racing manager, drove a 190 D the 14,045 km from Algiers to Cape Town with Rainer Günzler beside him and won outright, averaging 80.6 km/h across 44 days; he later called it the slowest racing car of his career. Enlarged to two liters and 55 PS, the engine carried the W110 fintails as the 190 Dc and 200 D. The OM615 replaced it in cars in 1968, but a 2.2-liter version ran on in the Unimog 421 until 1988.