End of Life/Break in Production

August 1965 was the time of relatively major production changes for Mercedes-Benz passenger cars.

As part of these changes, 112 chassis 300SE sedans (finbacks) ceased production, being replaced by the 108 chassis 300SE sedan and the 109 chassis 300SEL. 112 chassis 300SE coupes and convertibles remained in production for a few more years.

The "break-in-production" in the 112 chassis cars was at serial number 008909. No more 112 chassis sedans were built after this point. Coupes and convertibles continued from serial number 008910, but incorporated a number of production changes, the most significant of which was a different rear axle design with larger brakes and wheels, and a reconfigured layout of the components mounted on the firewall.

As of this time, the 112 chassis 300SE Sedans were using engine type 189.986. When production of the 112 chassis 300SE Sedan ceased, so did production of the 189.986 engine. The 112 chassis 300SE coupes and convertibles continued to use engine type 189.987.

The new 109 chassis 300SEL Sedan used the new engine type 189.988, and the new 108 chassis 300SE used the new engine type 189.989. The primary difference between these two new engines was that the 189.988 engine continued to support the air compressor for the air suspension of the 300SEL, and the 189.989 engine had no provisions for the air compressor since the 108 chassis 300SE Sedan had a coil spring suspension instead of air suspension.

Internally, the new engines where very similar to the previous 189.986 engine. Externally there were a number of visible differences. The two-piece oil/sump pan was replaced with a one-piece cast aluminum part, the intake manifold had two new rubber mounted weights suspended from the bottom rear surface of the plenum (for vibration damping), and the steel water pipe from the cylinder head to the water pump now had another, smaller, steel pipe welded to it. This pipe accommodated a "re-plumbed" routing of the coolant lines for the car's heater.

I can't determine exactly when it occurred, but later 189.988 and 189.989 had a re-routed fuel supply line to the injection pump. Originally, the steel line ran from the fuel filter canister, up between the engine and the injection pump, and connected to the injection pump on the engine side of the pump. Later engines changed this so that the supply line came up the outside of the injection pump. The inlet and outlet bores on the pump were also moved to the outside.