The Straight-Six Returns

The "S-Class," Mercedes-Benz's flagship saloon, needs no introduction. The current model, launched in 2013, became a hit with over 300,000 units sold worldwide, based on its concept of "innovative intelligent drive," "ultimate comfort," and "thorough efficiency improvement."

The 2017 minor change further evolved its safety features and communication functions, such as Intelligent Drive and Mercedes me connect, revitalizing it as a prestige car for a new era.

And the "S400d 4MATIC," which we test drove, was newly added to the lineup in September 2018. As the "d" in its name suggests, the engine is diesel, and the new model's highlight is its inline six-cylinder layout, a departure from the V6.

For about 20 years, Mercedes had stopped using the inline multi-cylinder engine layout in its models, as its elongated form in the front-rear direction was considered a disadvantage in terms of crash safety. However, with modern engines requiring more auxiliary components for environmental and fuel efficiency reasons, V-engines necessitate two banks of cylinders, increasing weight. Advances in technology have allowed for thinner cylinder walls, enabling the design of compact inline-six engines. This, along with improved body crash safety and the elimination of auxiliary belts, has led to its revival.

The 3.0-liter "OM 656" inline six-cylinder diesel turbo engine in the S400d 4MATIC produces a maximum output of 250 kW (340 ps) at 3,600-4,400 rpm and a maximum torque of 700 Nm at 1,200-3,200 rpm. It is a modular engine that shares its basic design with the gasoline "M256" inline-six found in the "S450." Its length is made compact by a cylinder pitch of 90 mm and a cylinder wall thickness of 8 mm. Different materials are used, with an aluminum cylinder block and steel pistons, and the cylinder walls feature NANOSLIDE friction-reducing coating.

Torque is supplied to all four wheels via the latest electronically controlled 9-speed automatic transmission, allowing this stately vehicle, measuring 5,155 mm in length, 1,915 mm in width, and 1,495 mm in height, with a curb weight of 2,150 kg, to run with absolutely no stress.

Page02.Sustained Acceleration That Makes You Feel You're Driving a "Good Car"

Sustained Acceleration That Makes You Feel You're Driving a "Good Car"

Starting the engine, the S-Class's characteristic thorough sound insulation is evident, and the rattling diesel noise is barely noticeable. On the road, the smooth, tuned power delivery, typical of an inline multi-cylinder engine, is pleasing, and the ample torque available from low revs, a hallmark of diesel engines, feels reassuring. When accelerating on a long uphill merge onto the highway, while it lacks the sheer power of a V8 S-Class, the sustained acceleration makes you keenly feel that you are driving a "good car."

At 100 km/h, the tachometer shows a mere 1,100 rpm (in 8th gear). Given that it runs on diesel, the fuel economy must be considerable (JC08 mode fuel economy is 13.3 km/h). While V8 S560 or V12 S600 models might be chosen for chauffeur-driven use, for those selecting an S-Class for personal use, the S400d, considering its economy, might just be the best grade.

The excellent visibility and ease of judging the car's dimensions, a hallmark of Mercedes models, allow the owner behind the wheel to enjoy a confident drive.

In terms of safety, the latest adaptive cruise control can be activated with a single button on the left spoke of the steering wheel. It accurately follows the car ahead while maintaining its lane position and smoothly navigates corners. With hands lightly on the wheel in the quiet cabin, one can experience a glimpse of the near future, imagining what the world of autonomous driving will be like.

The interior, with its large displays, leather, and wood, remains refreshingly cohesive, creating a comfortable and reassuring space. The three-pointed star on the hood's tip is a welcome touch for long-time Mercedes fans. The price is 11.6 million yen. The test car, equipped with optional Leather Package and AMG Line, totaled 14,539,200 yen.