2006-2009 Mercedes-Benz S-class Long (V221) S 420 CDI V8 (320 Hp) 7G-TRONIC

The Mercedes-Benz S 420 CDI, part of the long-wheelbase (V221) S-Class generation produced from October 2006 to April 2009, represented a compelling blend of luxury, performance, and diesel efficiency. Positioned as a mid-to-upper tier offering within the V221 range, it catered to buyers seeking the prestige of the S-Class with the long-distance comfort and fuel economy benefits of a V8 diesel engine. This variant was primarily marketed in Europe and other regions where diesel engines held significant market share, offering a sophisticated alternative to gasoline-powered S-Class models.

Technical Specifications

INTRODUCTION

The S 420 CDI, launched in late 2006, was a key component of the V221 S-Class’s appeal. The V221 generation (2005-2013) represented a significant leap forward in Mercedes-Benz technology, introducing features like Pre-Safe brake assist and advanced suspension systems. The “Long” designation indicated an extended wheelbase, providing increased rear passenger legroom, a feature particularly valued in markets like China and Germany. The S 420 CDI aimed to deliver the S-Class experience with improved fuel efficiency compared to its gasoline counterparts, appealing to drivers who prioritized both luxury and economy.

Powertrain & Engine Architecture

At the heart of the S 420 CDI lies the OM 629.911, a 4.0-liter V8 diesel engine. This engine is characterized by its robust construction and advanced technology for the time. It utilizes a common rail direct injection system, delivering fuel at extremely high pressure for optimized combustion. The engine also features a bi-turbocharger setup with an intercooler, enhancing both power and torque output. The valvetrain employs Double Overhead Camshafts (DOHC) with four valves per cylinder, contributing to efficient gas exchange. The engine’s 17:1 compression ratio is typical for a diesel engine, maximizing thermal efficiency. Paired with the engine is Mercedes-Benz’s 7G-TRONIC automatic transmission, a seven-speed unit known for its smooth shifting and efficiency. This transmission offered selectable driving modes, allowing drivers to tailor the shift points to their preferences.

Driving Characteristics

The S 420 CDI offered a distinctly different driving experience compared to the higher-horsepower S-Class variants. While not as overtly sporty, the 320 hp and substantial 730 Nm (538 lb-ft) of torque provided ample power for effortless cruising and confident overtaking. The 7G-TRONIC transmission was well-matched to the engine’s characteristics, providing smooth and timely gear changes. The long wheelbase and air suspension contributed to a remarkably comfortable ride, absorbing bumps and imperfections in the road with ease. Acceleration from 0-60 mph was achieved in approximately 6.3 seconds, respectable for a large luxury sedan. The emphasis was on relaxed, refined performance rather than outright speed.

Equipment & Trim Levels

The S 420 CDI typically came well-equipped, reflecting its position within the S-Class hierarchy. Standard features included leather upholstery, automatic climate control, a premium audio system, and a host of safety features like ABS, traction control, and multiple airbags. The long wheelbase model prioritized rear passenger comfort, often including features like reclining rear seats, a rear entertainment system, and individual climate controls. Optional extras included features like a panoramic sunroof, upgraded leather, and advanced driver-assistance systems like Distronic adaptive cruise control.

Chassis & Braking

The V221 S-Class featured an independent multi-link suspension system at both the front and rear, enhanced by air suspension. This setup provided a superior ride quality and allowed for adjustable ride height. The S 420 CDI was equipped with ventilated disc brakes on all four wheels, providing ample stopping power. The braking system was further enhanced by ABS (Anti-lock Braking System) and electronic brake-force distribution. Stabilizer bars were fitted front and rear to minimize body roll during cornering.

Market Reception & Comparison

The S 420 CDI was generally well-received by automotive critics, who praised its blend of luxury, performance, and fuel efficiency. It was often seen as a more sensible alternative to the gasoline-powered S-Class models, particularly for drivers who covered long distances. Compared to the S 500, the S 420 CDI offered similar levels of luxury but with significantly better fuel economy. Against other diesel-powered luxury sedans of the time, the S 420 CDI stood out for its refinement and advanced technology. However, some critics noted that the diesel engine lacked the smoothness and responsiveness of its gasoline counterparts.

Legacy

The OM 629 engine family, including the OM 629.911 found in the S 420 CDI, is known for its durability and longevity. With proper maintenance, these engines can reliably exceed 200,000 miles. Today, the S 420 CDI represents a compelling value proposition in the used car market, offering a luxurious and well-equipped sedan at a fraction of its original price. However, potential buyers should be aware of the higher maintenance costs associated with a complex vehicle like the S-Class, and the potential for age-related issues with components like the air suspension system. Despite these considerations, the S 420 CDI remains a desirable and capable luxury car, embodying the best of Mercedes-Benz engineering from the mid-2000s.