M123

The W123 of 1976 carried over most of its engines; the 2,525 cc M123 for the 250 and 250 T was the exception. It still showed its ancestry — a crankshaft on only four main bearings, an inclined shaft at the nose driving oil pump, fuel pump and distributor — but the cylinders were no longer cast in pairs, and the walls between them were sawn with slots for coolant rather than fully jacketed. Feeding it was the Solex 4A1, a four-barrel register carburetor shared with the W114 280 and about as intricate as the type ever became.

It met its brief. Against the 280 carburetor cars, which could pass 17 liters per 100 km around town, it was clearly more frugal, and a 1979 revision took it from 129 to 140 PS with the 1981 Energiekonzept update raising compression again. Then the M102 four appeared in the 200 and 230 E, doing nearly everything better on considerably less fuel, and interest collapsed. The estate was dropped in 1982 and the saloon lasted to 1985 selling almost nothing. The M103 that followed in 1984 was lighter, cheaper to build, stronger and smoother still.