The Mercedes-Benz S 450 CDI, produced from 2009 to 2010, was a variant of the W221 S-Class facelift, representing a compelling blend of luxury, performance, and fuel efficiency. Positioned as a mid-to-upper range offering within the S-Class lineup, it catered to buyers seeking a powerful diesel engine and the refined experience synonymous with the S-Class nameplate. This model year saw a significant refresh of the W221 generation, incorporating updated styling, technology, and engine options, with the S 450 CDI standing out as a particularly strong performer in the diesel segment. It was built on the 1HX0 platform, shared with other high-end Mercedes-Benz vehicles of the era.
Powertrain & Engine Architecture
The heart of the S 450 CDI is the OM 629.911 4.0-liter V8 diesel engine. This engine is a sophisticated design featuring a commonrail direct fuel injection system, delivering precise fuel metering for optimal combustion and reduced emissions. The engine boasts a relatively high compression ratio of 17:1, contributing to its efficiency and power output. A turbocharger with an intercooler further enhances performance by forcing more air into the cylinders. The engine produces 320 horsepower at 3600 rpm and a substantial 730 Nm (538.42 lb-ft) of torque at 2200 rpm. This torque figure is particularly noteworthy, providing effortless acceleration and strong pulling power.
Paired with the engine is the 7G-TRONIC seven-speed automatic transmission. This transmission is known for its smooth and responsive shifting characteristics. It utilizes a torque converter for smooth launches and a planetary gearset for efficient power transfer. The 7G-TRONIC offers both fully automatic operation and a manual shift mode, allowing the driver to exert more control over gear selection. The transmission’s gear ratios are tuned to balance performance and fuel economy, maximizing the engine’s torque output across a wide range of driving conditions.
Engine Specifications
The OM 629.911 engine is a robust and well-engineered unit, designed for longevity and reliability. It incorporates features such as a reinforced crankshaft, optimized piston design, and advanced cooling systems to withstand the stresses of high performance. The engine oil capacity is 10.5 liters (11.1 US qt / 9.24 UK qt), and Mercedes-Benz specifies a particular oil grade to ensure optimal lubrication and protection.
Driving Characteristics
The S 450 CDI delivers a driving experience characterized by smooth power delivery and effortless cruising. The high torque output of the diesel engine means that strong acceleration is available from low engine speeds, making overtaking and merging onto highways a breeze. While not as overtly sporty as some of the gasoline-powered S-Class variants, the S 450 CDI offers a refined and comfortable ride. The 7G-TRONIC transmission contributes to this smoothness, providing seamless gear changes that are virtually imperceptible. Compared to the S 550 (gasoline V8), the S 450 CDI prioritizes torque and fuel efficiency over outright horsepower and responsiveness. It also differs significantly from the S 350 CDI, offering a substantial power upgrade and a more luxurious experience.
The weight distribution of the S 450 CDI, combined with the sophisticated suspension system, results in stable and predictable handling. The car feels planted and secure, even at high speeds. The steering is precise and well-weighted, providing good feedback to the driver.
Equipment & Trim Levels
As a flagship luxury sedan, the S 450 CDI came standard with a comprehensive array of features. These included leather upholstery, wood trim, a premium sound system, automatic climate control, power-adjustable seats with memory function, and a host of safety features such as ABS, traction control, and multiple airbags. The S-Class was renowned for its advanced technology, and the S 450 CDI was no exception, offering features like a COMAND infotainment system with navigation, parking assist, and adaptive cruise control.
Optional extras included features such as a panoramic sunroof, upgraded leather upholstery, rear-seat entertainment system, and a more powerful sound system. The S 450 CDI could also be equipped with features like massaging seats and a refrigerator in the rear center console, further enhancing the luxury experience.
Chassis & Braking
The S 450 CDI features a fully independent suspension system, with multi-link suspension at all four corners. This suspension design provides a comfortable ride while maintaining good handling characteristics. The suspension is electronically controlled, allowing the car to adjust its damping characteristics based on road conditions and driving style. The car utilizes disc brakes on all four wheels, providing ample stopping power. The braking system is equipped with ABS (Anti-lock Braking System) and Electronic Brakeforce Distribution (EBD) to enhance safety and stability. The standard tire size is 255/45 R18, mounted on 18-inch alloy wheels.
Market Reception & Comparison
The S 450 CDI was generally well-received by automotive critics. It was praised for its powerful and efficient diesel engine, luxurious interior, and refined driving experience. Critics noted that the S 450 CDI offered a compelling alternative to the gasoline-powered S-Class variants, particularly for drivers who prioritize fuel economy and torque. Compared to the S 350 CDI, the S 450 CDI offered a significant performance upgrade, while still maintaining excellent fuel efficiency. However, some critics noted that the diesel engine was slightly noisier than the gasoline engines. In terms of reliability, the OM 629 engine family is generally considered to be robust and durable, although regular maintenance is essential to ensure long-term reliability.
Technical Specifications
| Body Type | Sedan, 4 Doors, 5 Seats |
| Fuel Economy (Combined) | 9.1-9.3 l/100 km (25.8 – 25.3 US mpg, 31 – 30.4 UK mpg, 11 – 10.8 km/l) |
| CO2 Emissions | 240-245 g/km |
| Maximum Speed | 250 km/h (155.34 mph) |
| Acceleration 0-100 km/h | 6.6 sec |
| Acceleration 0-60 mph | 6.3 sec |
| Power | 320 Hp @ 3600 rpm |
| Torque | 730 Nm @ 2200 rpm (538.42 lb.-ft. @ 2200 rpm) |
| Engine Layout | Front, Longitudinal |
| Engine Model/Code | OM 629.911 |
| Engine Displacement | 3996 cm3 (243.85 cu. in.) |
| Number of Cylinders | 8 |
| Engine Configuration | V-engine |
| Compression Ratio | 17:1 |
| Fuel Injection System | Diesel Commonrail |
| Engine Oil Capacity | 10.5 l (11.1 US qt | 9.24 UK qt) |
| Kerb Weight | 2015 kg (4442.31 lbs.) |
| Max. Weight | 2690 kg (5930.43 lbs.) |
| Trunk (Boot) Space | 560 l (19.78 cu. ft.) |
| Fuel Tank Capacity | 90 l (23.78 US gal | 19.8 UK gal) |
| Length | 5096 mm (200.63 in.) |
| Width | 1871 mm (73.66 in.) |
| Height | 1479 mm (58.23 in.) |
| Wheelbase | 3035 mm (119.49 in.) |
| Number of Gears & Gearbox Type | 7 gears, automatic transmission G-TRONIC |
Legacy
The S 450 CDI, while only produced for a short period, has become a sought-after model among S-Class enthusiasts. The OM 629 engine is known for its durability and relatively low maintenance costs, making it a practical choice for long-term ownership. However, as with any older vehicle, regular maintenance and attention to detail are essential to keep it running smoothly. Today, well-maintained examples of the S 450 CDI can command a premium in the used car market, appealing to buyers who appreciate its blend of luxury, performance, and fuel efficiency. The model represents a high point in Mercedes-Benz’s diesel technology, offering a refined and capable driving experience that continues to impress even by modern standards.
