The Mercedes Benz M186 Engine was a 3.0–litre single overhead camshaft inline-6 developed in the early 1950s to power the company's new flagship 300 "Adenauer" (W186) four-door saloon.

Variants of the M186 went on to be used in the exclusive 300 S/300 Sc gran tourer, W194 300SL racer, iconic gullwing 300SL sports car, and Mercedes top-end 300-series sedans and limousines, and coupes of the early to mid-1960s.

Designed to give reliable service under prolonged hard use, the engine featured deep water jackets, thermostatically controlled oil cooling, copper-lead bearings, and a hardened crankshaft.

[7] Similar to the M198 used in the production 300SL, the engine is titled 50 degrees to the left in order to reduce the height of the hood, and uses a dry sump lubrication system instead of an oil pan and reservoir.

[12] In order to deliver track-ready performance, race-derived features were built in, including a dry sump lubrication system and Bosch mechanical direct fuel-injection, one of the first production cars with fuel injection.

A significantly detuned direct-injection, dry sump oil system engine was used in the late W188 300 Sc of 1955 to 1958 producing 175 hp (130 kW) at 5400 rpm and 8.55:1 compression ratio