The Mercedes-Benz S 350d (W223), introduced in May 2023 and produced through 2026, represents a diesel-powered variant within the sixth generation (W223) of the flagship S-Class sedan. This model occupies a position between the entry-level S 350 and the higher-performance S 580, offering a blend of luxury, efficiency, and moderate performance. It features a mild hybrid system (EQ Boost) paired with a nine-speed automatic transmission (9G-TRONIC), designed to enhance fuel economy and refinement. The W223 generation S-Class, built on an updated version of the MRA (Modular Rear-wheel-drive Architecture) platform, prioritizes technological innovation and passenger comfort.
Powertrain & Engine Architecture
The S 350d is powered by the OM 656.830, a 2.989-liter (182.4 cu. in.) inline-six cylinder diesel engine. This engine is a key component of Mercedes-Benz’s modular engine family, known for its robust construction and advanced technology. It utilizes a sophisticated diesel commonrail fuel injection system, delivering fuel at extremely high pressure for optimized combustion. The engine features a bi-turbocharger setup with an intercooler, providing both low-end torque and high-end power. The valvetrain employs Double Overhead Camshafts (DOHC) with four valves per cylinder, contributing to efficient gas exchange. The compression ratio is a high 15.5:1, typical for modern diesel engines designed for efficiency.
Central to the S 350d’s powertrain is its 48-volt mild hybrid system, branded as EQ Boost. This system incorporates a 23 hp (17 kW) electric motor integrated between the engine and the 9G-TRONIC transmission. The electric motor doesn’t provide full electric drive capability but assists the engine during acceleration, smoothing out power delivery and reducing load. The system also enables features like ‘glide sailing’ where the engine shuts off during coasting to conserve fuel. The 0.9 kWh lithium-ion battery powers the EQ Boost system. The 9G-TRONIC automatic transmission is a nine-speed unit known for its smooth shifting and wide gear ratio spread. It’s designed to optimize fuel efficiency and provide comfortable cruising at highway speeds.
Engine Specifications
The OM 656.830 engine produces 313 hp at 3600-4800 rpm and a substantial 650 Nm (479.42 lb-ft) of torque between 1200-3200 rpm. This broad torque curve provides strong acceleration in real-world driving conditions. The engine oil capacity is 9 liters (9.51 US qt / 7.92 UK qt), and it requires a specific oil specification as defined by Mercedes-Benz. The engine also incorporates a particulate filter to reduce emissions, meeting Euro 6e standards.
Driving Characteristics
The S 350d delivers a refined and comfortable driving experience. The combination of the inline-six diesel engine and the 9G-TRONIC transmission results in smooth and effortless acceleration. While not as overtly sporty as the higher-powered S-Class variants, the S 350d offers a 0-100 km/h (0-62 mph) time of 5.6 seconds, which is more than adequate for most drivers. The EQ Boost system contributes to a responsive feel, particularly during initial acceleration. The wide gear ratio spread of the 9G-TRONIC transmission allows for relaxed highway cruising at low engine speeds, further enhancing fuel efficiency. The rear-wheel drive configuration provides a balanced handling characteristic, although it may not offer the same level of all-weather capability as all-wheel-drive models.
Compared to the gasoline-powered S 450 or the more potent S 580, the S 350d prioritizes fuel economy and torque delivery over outright horsepower. The diesel engine’s strong low-end torque makes it well-suited for effortless overtaking and relaxed long-distance driving. Manual transmission options are not available for this model, focusing solely on the automatic for a premium experience.
Equipment & Trim Levels
The S 350d, as a flagship model, comes standard with a comprehensive array of luxury features. Standard equipment typically includes leather upholstery, heated and ventilated front seats with massage functions, a Burmester surround sound system, a large touchscreen infotainment system (MBUX), and a suite of advanced driver-assistance systems (ADAS). These ADAS features include adaptive cruise control, lane-keeping assist, automatic emergency braking, and a 360-degree camera system.
Optional extras for the S 350d are extensive and can include features such as a head-up display, rear-seat entertainment system, premium leather options, and various interior trim packages. The interior dashboard configuration is characterized by a minimalist design with a large central touchscreen and a digital instrument cluster. The ambient lighting system allows for customization of the cabin’s atmosphere. Air suspension is standard, providing a supremely comfortable ride quality.
Chassis & Braking
The W223 S-Class utilizes an independent multi-link suspension system at both the front and rear axles. The standard suspension incorporates air suspension, which provides adjustable ride height and damping characteristics. This allows the driver to tailor the ride quality to their preferences. The S 350d features ventilated disc brakes on all four wheels, providing ample stopping power. Anti-lock Braking System (ABS) is standard, along with electronic stability control. An optional 4-wheel steering system (4WS) is available, enhancing maneuverability at low speeds and stability at high speeds. The steering system is an electric power steering rack and pinion system.
Market Reception & Comparison
The S 350d was generally well-received by automotive critics, who praised its blend of luxury, efficiency, and refinement. The diesel engine was noted for its quiet operation and strong torque delivery. Fuel economy figures range from 5.9 to 6.8 l/100 km (39.9 – 34.6 US mpg / 47.9 – 41.5 UK mpg), making it a relatively efficient option within the S-Class range. Compared to the gasoline-powered S 450, the S 350d offers superior fuel economy but slightly less overall performance. Reliability reports suggest that the OM 656 engine family is generally robust, although diesel engines can be more susceptible to issues related to the emissions control system (e.g., particulate filter).
Technical Specifications
| Body type | Sedan, 4 Doors, 5 Seats |
| Fuel economy | 5.9-6.8 l/100 km (39.9 – 34.6 US mpg, 47.9 – 41.5 UK mpg, 16.9 – 14.7 km/l) |
| CO2 emissions | 154-178 g/km |
| Emission standard | Euro 6e |
| Acceleration 0-100 km/h | 5.6 sec |
| Acceleration 0-60 mph | 5.3 sec |
| Maximum speed | 250 km/h (155.34 mph) |
| Engine displacement | 2989 cm3 (182.4 cu. in.) |
| Number of cylinders | 6, Inline |
| Power | 313 Hp @ 3600-4800 rpm |
| Torque | 650 Nm @ 1200-3200 rpm (479.42 lb-ft @ 1200-3200 rpm) |
| Engine Model/Code | OM 656.830 |
| Transmission | 9 gears, automatic transmission G-TRONIC |
| Kerb Weight | 2015 kg (4442.31 lbs.) |
| Max. weight | 2730 kg (6018.62 lbs.) |
| Trunk (boot) space | 540 l (19.07 cu. ft.) |
| Fuel tank capacity | 65 l (17.17 US gal, 14.3 UK gal) |
Legacy
The OM 656 engine family, including the version used in the S 350d, has proven to be a reliable and durable powertrain. While modern diesel engines are subject to increasingly stringent emissions regulations, the OM 656 has generally met these standards effectively. In the used car market, the S 350d represents a compelling value proposition for buyers seeking a luxurious and efficient sedan. The mild hybrid system contributes to improved fuel economy and reduced emissions, making it a more environmentally friendly option compared to older diesel models. However, potential buyers should be aware of the potential for issues related to the diesel particulate filter and other emissions control components, and ensure that the vehicle has been properly maintained.
