OM617

It began as an OM616 with a fifth cylinder, launched in 1974 in the 240 D 3.0 and carried into the W123 as the 300 D. Then in 1976 Daimler-Benz hung a turbocharger on it for the C111-IID research coupé, which took sixteen world speed and endurance marks at Nardò; a 230 PS development in the C111-III added nine more in 1978. The production consequence appeared that May as the 300 SD, sold only in the United States and Canada, and built expressly so that Mercedes-Benz could lift its fleet average against the Corporate Average Fuel Economy rules that began to bite in 1978. It was the first turbodiesel saloon anyone had put into series production.

Turbocharging brought oil jets spraying the underside of the pistons, stronger connecting rods, sodium-filled valve stems, a nitride-hardened crankshaft and a chain-driven oil pump of its own. There was no intercooler; even so, specific fuel consumption improved by roughly 20 g/kWh over the naturally aspirated engine, and Road & Track measured 25 mpg from a two-ton luxury saloon. Around 28,000 W116 300 SDs were sold. The wider reputation followed from the unblown versions in the 300 D and 300 TD, plenty of which have passed a million kilometers without being opened, and the engine finished its career in the 300 GD, the T1 vans and the Swedish Bandvagn 206.