2020-2023 Mercedes-Benz S-class (W223) S 350d (286 Hp) 9G-TRONIC

The Mercedes-Benz S 350d (W223), produced from 2020 to April 2023, represents a diesel-powered variant within the sixth generation (W223) of the flagship S-Class sedan. Positioned as a mid-range offering in the W223 lineup, it served as a more fuel-efficient alternative to the gasoline-powered S 450 and the high-performance S 580 models, while offering a similar level of luxury and technology. The S 350d was designed to appeal to buyers prioritizing long-distance comfort, refined driving dynamics, and lower running costs compared to its more powerful siblings. It utilizes the 1HX0 chassis, shared with other high-end Mercedes-Benz models.

Powertrain & Engine Architecture

The S 350d is powered by the OM 656.929, a 2.9-liter inline-six cylinder diesel engine. This engine is a significant departure from the V6 diesel engines previously used in the S-Class, representing a move towards modular engine designs within the Mercedes-Benz portfolio. The OM 656 features a steel crankshaft, aluminum engine block, and a cam-in-head valvetrain with four valves per cylinder (DOHC). A key innovation is the use of a stepped combustion process, designed to reduce particulate emissions and improve efficiency. The engine employs a two-stage turbocharging system – a small turbocharger for immediate response at low engine speeds and a larger turbocharger for increased power at higher RPMs. This BiTurbo setup, coupled with an intercooler, contributes to both strong low-end torque and sustained high-speed performance.

Fuel is delivered via a common rail direct injection system operating at extremely high pressures (2,700 bar), ensuring precise fuel atomization and efficient combustion. The S 350d is exclusively paired with Mercedes-Benz’s 9G-TRONIC nine-speed automatic transmission. This transmission is known for its smooth shifting characteristics and wide gear ratio spread, contributing to both fuel economy and refined cruising. The 9G-TRONIC features a torque converter lockup clutch that engages across multiple gears, minimizing slippage and further enhancing efficiency. The transmission is electronically controlled and adapts its shift points based on driving style and road conditions.

Driving Characteristics

The S 350d delivers a distinctly different driving experience compared to the higher-output S-Class variants. While it doesn’t offer the outright acceleration of the S 580, the 600 Nm (442.54 lb-ft) of torque available from 1200-3200 rpm provides ample power for effortless overtaking and comfortable highway cruising. The 9G-TRONIC transmission is programmed to prioritize smooth shifts and fuel efficiency, resulting in a relaxed and refined driving experience. The lower gear ratios provide brisk acceleration from a standstill, while the higher gears allow for exceptionally quiet and efficient operation at highway speeds. Compared to a hypothetical manual transmission version (not offered), the 9G-TRONIC minimizes driver workload and maximizes comfort, aligning with the S-Class’s luxury positioning. The engine is remarkably quiet for a diesel, with effective noise insulation minimizing intrusion into the cabin. The rear-wheel drive configuration contributes to balanced handling, although all-wheel drive (4MATIC) was available as an option.

Equipment & Trim Levels

The S 350d came standard with a comprehensive array of luxury features, befitting its flagship status. Standard equipment typically included leather upholstery, heated and ventilated front seats with massage functions, a Burmester surround sound system, a large dual-screen display incorporating the MBUX infotainment system, and a panoramic sunroof. The MBUX system offered voice control, augmented reality navigation, and a host of connectivity features. Interior trim options included a variety of wood veneers, aluminum accents, and leather finishes. Optional extras included rear-seat entertainment systems, premium leather packages, and advanced driver-assistance systems such as adaptive cruise control, lane-keeping assist, and automatic parking. The S 350d was often specified with the AMG Line package, which added sportier exterior styling elements and interior trim.

Chassis & Braking

The W223 S-Class, including the S 350d, utilizes a sophisticated chassis design focused on ride comfort and handling balance. The front suspension features an independent multi-link setup with air suspension, providing a smooth and controlled ride. The rear suspension also employs an independent multi-link design with air suspension, and importantly, includes Mercedes-Benz’s E-ACTIVE BODY CONTROL system on many models. This system uses active suspension dampers and a 48-volt electrical system to continuously adjust the suspension based on road conditions and driving style, minimizing body roll and maximizing ride comfort. Braking duties are handled by ventilated discs on all four wheels. The S 350d is equipped with ABS (Anti-lock Braking System), electronic brake-force distribution, and brake assist. Larger brake rotors were available as an option for improved stopping power. The steering system is a rack-and-pinion setup with electric power assistance, providing precise and responsive steering feel.

Market Reception & Comparison

The S 350d was generally well-received by automotive critics, who praised its refined driving experience, luxurious interior, and impressive fuel economy. It was often cited as the sweet spot in the S-Class range, offering a compelling blend of performance, comfort, and efficiency. Compared to the S 450, the S 350d offered significantly better fuel economy, making it a more practical choice for high-mileage drivers. However, the S 450 provided more powerful acceleration and a slightly more engaging driving experience. Compared to the S 580, the S 350d represented a more affordable entry point into the S-Class range, while still delivering a high level of luxury and technology. Fuel economy figures ranged from 6.4 to 7.7 l/100 km (36.8 – 30.5 US mpg), depending on driving conditions and equipment. Reliability reports have generally been positive, with the OM 656 engine proving to be a robust and durable unit.

Technical Specifications

Legacy

The OM 656 engine, as featured in the S 350d, has proven to be a reliable and durable powertrain. Its advanced technology, including the stepped combustion process and two-stage turbocharging, contributes to both efficiency and longevity. On the used car market, the W223 S 350d represents a compelling value proposition, offering a high level of luxury and technology at a more accessible price point than its higher-output siblings. The combination of a comfortable ride, refined driving dynamics, and impressive fuel economy makes it a popular choice among buyers seeking a long-distance cruiser. While diesel engines have faced increasing scrutiny in recent years, the S 350d’s advanced emissions control systems help it meet stringent environmental standards. The W223 S 350d is likely to remain a desirable and sought-after luxury sedan for years to come.