The Mercedes-Benz S 350d (W222 facelift, produced from 2017 to 2020) represents a significant iteration of the flagship S-Class sedan, positioned as a diesel-powered alternative within the broader range. This variant aimed to deliver the luxury and technological sophistication expected of the S-Class, combined with improved fuel efficiency and strong torque output. It occupied a middle ground in the W222 lineup, offering a balance between the entry-level S 350d and the higher-performance S 500 and AMG models. The facelift, introduced in 2017, brought styling revisions, updated technology, and refinements to the engine and transmission.
Powertrain & Engine Architecture
The S 350d is powered by the OM 656.929, a 2.9-liter inline-six cylinder diesel engine. This engine marked a departure from the previous V6 diesel configurations used in the S-Class, representing a new generation of Mercedes-Benz diesel engines. The OM 656 features a stepped combustion process, designed to optimize efficiency and reduce emissions. It utilizes a commonrail direct fuel injection system operating at extremely high pressures (2,700 bar) for precise fuel delivery and improved combustion. The engine also incorporates a variable geometry turbocharger with water cooling and an intercooler to enhance power and responsiveness. The compression ratio is a high 15.5:1, contributing to the engine’s thermal efficiency.
The engine is paired with the 9G-TRONIC nine-speed automatic transmission. This transmission is known for its smooth shifting, wide gear ratio spread, and contribution to fuel economy. The 9G-TRONIC allows the engine to operate within its optimal efficiency range more frequently, further enhancing fuel savings. The transmission features a torque converter lockup clutch that engages in most gears, minimizing energy loss. The drivetrain is rear-wheel drive as standard, with 4MATIC all-wheel drive available as an option.
Engine Specifications
The OM 656.929 engine produces 286 horsepower at 3,400-4,600 rpm and a substantial 600 Nm (442.54 lb-ft) of torque between 1,200-3,200 rpm. This broad torque curve provides strong acceleration and effortless cruising. The engine’s power-to-liter ratio is 97.8 hp/liter, demonstrating its efficiency. The engine also incorporates a particulate filter to reduce emissions, meeting Euro 6 standards.
Driving Characteristics
The S 350d delivers a refined and comfortable driving experience. The high torque output of the diesel engine provides strong acceleration from low speeds, making it well-suited for city driving and overtaking maneuvers. While not as overtly sporty as the gasoline-powered S 500, the S 350d offers ample performance for most drivers. The 0-62 mph (0-100 km/h) acceleration is quoted at 6 seconds, and 0-60 mph is calculated at 5.7 seconds. The 9G-TRONIC transmission contributes to smooth and seamless gear changes, enhancing the overall driving experience. The gear ratios are optimized for both fuel efficiency and performance, with a tall ninth gear for relaxed highway cruising.
Compared to the S 500, the S 350d offers a more relaxed and fuel-efficient driving experience. The S 500, with its larger gasoline engine, provides more outright power and a sportier character. However, the S 350d’s diesel engine delivers significantly better fuel economy, making it a more practical choice for long-distance driving. Compared to earlier S-Class diesel models, the OM 656 engine is noticeably quieter and more refined, minimizing the typical diesel engine clatter.
Equipment & Trim Levels
The S 350d, as a flagship model, came standard with a comprehensive array of luxury features. Standard equipment typically included leather upholstery, heated and ventilated front seats with massage functions, a premium Burmester surround sound system, a large infotainment display with Mercedes-Benz’s COMAND system, and a suite of advanced driver-assistance systems such as adaptive cruise control, lane-keeping assist, and automatic emergency braking. Interior trim options included various wood veneers, aluminum accents, and leather color choices.
Optional extras included features such as a rear-seat entertainment system, a panoramic sunroof, upgraded leather upholstery, and various styling packages. The S 350d was often specified with the AIRMATIC suspension system, which provides adjustable ride height and damping for enhanced comfort and handling. The Executive Rear Seat Package was also a popular option, adding features such as reclining rear seats, a massage function, and a rear-seat control panel.
Chassis & Braking
The S 350d utilizes an independent multi-link suspension system at both the front and rear axles. This suspension design provides a comfortable ride and precise handling. The AIRMATIC suspension, when equipped, further enhances ride quality by automatically adjusting the damping and ride height based on road conditions and driving style. The steering system is a rack-and-pinion type with electric power assistance.
The braking system consists of ventilated discs at all four wheels. The anti-lock braking system (ABS) and electronic stability program (ESP) are standard features, providing enhanced safety and control. Tire size is typically 245/55 R17, mounted on 17-inch alloy wheels, although larger wheel sizes were available as options.
Market Reception & Comparison
The S 350d was generally well-received by automotive critics. It was praised for its refined driving experience, luxurious interior, and impressive fuel economy. The diesel engine’s strong torque output was also a highlight, providing effortless performance. However, some critics noted that the S 350d lacked the outright performance of the gasoline-powered S 500.
In terms of fuel economy, the S 350d offered a significant advantage over its gasoline counterparts. Combined fuel consumption figures ranged from 5.1 to 5.4 l/100 km (46.1 to 43.6 US mpg or 55.4 to 52.3 UK mpg), making it a practical choice for long-distance drivers. CO2 emissions ranged from 134 to 139 g/km. Reliability reports generally indicate good reliability for the OM 656 engine and 9G-TRONIC transmission, although regular maintenance is essential.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | S-Class |
| Generation | S-Class (W222, facelift 2017) |
| Type (Engine) | S 350d (286 Hp) G-TRONIC |
| Start of production | 2017 |
| End of production | 2020 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Sedan |
| Seats | 4-5 |
| Doors | 4 |
| Fuel consumption at Low speed (WLTP) | 6.4 l/100 km (36.8 US mpg, 44.1 UK mpg, 15.6 km/l) |
| Fuel consumption at very high speed (WLTP) | 7.2 l/100 km (32.7 US mpg, 39.2 UK mpg, 13.9 km/l) |
| CO2 emissions (WLTP) | 167-189 g/km |
| Fuel consumption (economy) – urban | 6.4-6.5 l/100 km (36.8 – 36.2 US mpg, 44.1 – 43.5 UK mpg, 15.6 – 15.4 km/l) |
| Fuel consumption (economy) – extra urban | 4.4-4.7 l/100 km (53.5 – 50 US mpg, 64.2 – 60.1 UK mpg, 22.7 – 21.3 km/l) |
| Fuel consumption (economy) – combined | 5.1-5.4 l/100 km (46.1 – 43.6 US mpg, 55.4 – 52.3 UK mpg, 19.6 – 18.5 km/l) |
| CO2 emissions | 134-139 g/km |
| Fuel Type | Diesel |
| Acceleration 0 – 100 km/h | 6 sec |
| Acceleration 0 – 62 mph | 6 sec |
| Acceleration 0 – 60 mph | 5.7 sec |
| Maximum speed | 250 km/h (155.34 mph) |
| Emission standard | Euro 6 |
| Weight-to-power ratio | 6.6 kg/Hp, 150.9 Hp/tonne |
| Weight-to-torque ratio | 3.2 kg/Nm, 316.6 Nm/tonne |
| Power | 286 Hp @ 3400-4600 rpm |
| Torque | 600 Nm @ 1200-3200 rpm (442.54 lb.-ft. @ 1200-3200 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | OM 656.929 |
| Engine displacement | 2925 cm3 (178.49 cu. in.) |
| Number of cylinders | 6 |
| Engine configuration | Inline |
| Compression ratio | 15.5:1 |
| Fuel injection system | Diesel Commonrail |
| Engine oil capacity | 8.5 l (8.98 US qt | 7.48 UK qt) |
| Coolant | 13 l (13.74 US qt | 11.44 UK qt) |
| Kerb Weight | 1895 kg (4177.76 lbs.) |
| Max. weight | 2690 kg (5930.43 lbs.) |
| Max load | 795 kg (1752.67 lbs.) |
| Trunk (boot) space – minimum | 510 l (18.01 cu. ft.) |
| Fuel tank capacity | 70 l (18.49 US gal | 15.4 UK gal) |
| Length | 5141 mm (202.4 in.) |
| Width | 1905 mm (75 in.) |
| Height | 1498 mm (58.98 in.) |
| Wheelbase | 3035 mm (119.49 in.) |
| Drivetrain Architecture | Rear wheel drive |
| Number of gears and type of gearbox | 9 gears, automatic transmission G-TRONIC |
Legacy
The OM 656 engine, as used in the S 350d, has proven to be a robust and reliable powerplant. While diesel engines, in general, have faced increased scrutiny in recent years, the OM 656 has maintained a good reputation for durability and longevity. The 9G-TRONIC transmission has also proven to be a reliable unit. On the used car market, the S 350d represents a compelling value proposition, offering the luxury and technology of the S-Class at a more affordable price point than its gasoline-powered counterparts. However, potential buyers should ensure that the vehicle has been properly maintained and that the diesel particulate filter is functioning correctly.
