The Mercedes-Benz M-Class (W164) ML 420 CDI V8 4MATIC, produced from 2006 to 2008, represented a potent offering within the second generation of Mercedes’ mid-size luxury SUV. Positioned as a premium variant, it slotted above the ML 320 CDI and ML 350 models, offering significantly more performance thanks to its V8 diesel engine. The W164 M-Class, launched in 2005, aimed to address criticisms of the first-generation M-Class, offering improved refinement, interior space, and on-road dynamics while maintaining off-road capability. The ML 420 CDI was primarily marketed in Europe and other regions where diesel engines were favored, and was not officially sold in the United States.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | M-Class |
| Generation | M-Class (W164) |
| Type | ML 420 CDI V8 (306 Hp) 4MATIC 7G-TRONIC |
| Start of production | 2006 |
| End of production | 2008 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | SUV |
| Seats | 5 |
| Doors | 5 |
| Fuel consumption (urban) | 14.4-15 l/100 km (16.3 – 15.7 US mpg, 19.6 – 18.8 UK mpg, 6.9 – 6.7 km/l) |
| Fuel consumption (extra urban) | 9.1 l/100 km (25.8 US mpg, 31 UK mpg, 11 km/l) |
| Fuel consumption (combined) | 11.1-11.3 l/100 km (21.2 – 20.8 US mpg, 25.4 – 25 UK mpg, 9 – 8.8 km/l) |
| CO2 emissions | 294-299 g/km |
| Fuel Type | Diesel |
| Acceleration 0 – 100 km/h | 6.8 sec |
| Acceleration 0 – 62 mph | 6.8 sec |
| Acceleration 0 – 60 mph | 6.5 sec |
| Maximum speed | 225 km/h (139.81 mph) |
| Emission standard | Euro 4 |
| Weight-to-power ratio | 7.6 kg/Hp, 132.2 Hp/tonne |
| Weight-to-torque ratio | 3.3 kg/Nm, 302.4 Nm/tonne |
| Power | 306 Hp @ 3600 rpm |
| Power per litre | 76.6 Hp/l |
| Torque | 700 Nm @ 2000 rpm (516.29 lb.-ft. @ 2000 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | OM 629 DE 40 LA |
| Engine displacement | 3996 cm3 (243.85 cu. in.) |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Number of valves per cylinder | 4 |
| Fuel injection system | Diesel Commonrail |
| Engine aspiration | Turbocharger, Intercooler |
| Engine oil capacity | 11.5 l (12.15 US qt | 10.12 UK qt) |
| Coolant capacity | 12 l (12.68 US qt | 10.56 UK qt) |
| Kerb Weight | 2315 kg (5103.7 lbs.) |
| Max. weight | 2945 kg (6492.61 lbs.) |
| Max load | 630 kg (1388.91 lbs.) |
| Trunk (boot) space – minimum | 551 l (19.46 cu. ft.) |
| Trunk (boot) space – maximum | 2050 l (72.4 cu. ft.) |
| Fuel tank capacity | 95 l (25.1 US gal | 20.9 UK gal) |
| Length | 4780 mm (188.19 in.) |
| Width | 1911 mm (75.24 in.) |
| Height | 1815 mm (71.46 in.) |
| Wheelbase | 2915 mm (114.76 in.) |
| Front track | 1627 mm (64.06 in.) |
| Rear track | 1629 mm (64.13 in.) |
| Drive wheel | All wheel drive (4×4) |
| Number of gears | 7 |
| Gearbox type | Automatic transmission |
| Front suspension | Double wishbone |
| Rear suspension | Spring Strut |
| Front brakes | Ventilated discs |
| Rear brakes | Disc |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Tires size | 255/55 R19 |
Powertrain & Engine Architecture
The heart of the ML 420 CDI is the OM 629 DE 40 LA, a 4.0-liter V8 diesel engine. This engine utilizes a common rail direct injection system, delivering fuel at extremely high pressure for optimized combustion. The OM629 featured a single turbocharger with an intercooler to increase air density and boost power output. The engine produced 306 horsepower at 3600 rpm and a substantial 700 Nm (516 lb-ft) of torque at just 2000 rpm. This torque figure was a key characteristic, providing strong pulling power and effortless acceleration. The engine also featured four valves per cylinder and a robust engine block designed for longevity. Paired with the engine was the 7G-TRONIC automatic transmission, a seven-speed unit known for its smooth shifting and efficiency. This transmission offered both fully automatic operation and a manual shift mode for greater driver control.
Driving Characteristics
The ML 420 CDI offered a distinctly different driving experience compared to its gasoline-powered siblings. The abundant torque meant strong acceleration from low engine speeds, making it particularly well-suited for towing and navigating challenging terrain. While not as outright sporty as the ML 350, the ML 420 CDI provided a relaxed and confident driving experience. The 7G-TRONIC transmission contributed to this smoothness, with well-spaced gear ratios that kept the engine in its optimal power band. Compared to the ML 320 CDI, the V8 offered a noticeable increase in power and refinement. The ML 420 CDI’s weight, around 2315 kg (5103.7 lbs), was managed effectively by the engine’s torque, resulting in a 0-60 mph time of approximately 6.5 seconds.
Equipment & Trim Levels
The ML 420 CDI typically came well-equipped, reflecting its position as a premium model. Standard features included leather upholstery, automatic climate control, a premium audio system, and power-adjustable front seats. Optional extras included a sunroof, navigation system, upgraded wheels, and parking sensors. Interior trim options varied, with choices in wood and aluminum finishes. The dashboard layout was typical of Mercedes-Benz at the time, emphasizing a luxurious and functional design. The 4MATIC all-wheel-drive system was standard, providing enhanced traction and stability in all weather conditions.
Chassis & Braking
The W164 M-Class utilized a double wishbone front suspension and a spring strut rear suspension. This setup aimed to balance ride comfort with handling precision. The ML 420 CDI featured ventilated disc brakes at the front and solid discs at the rear. Anti-lock braking system (ABS) was standard, along with electronic stability control. The suspension was tuned to accommodate the vehicle’s weight and the engine’s torque, providing a stable and controlled ride. Stabilizer bars were fitted front and rear to reduce body roll during cornering.
Market Reception & Comparison
The ML 420 CDI was generally well-received by automotive critics, who praised its powerful engine, smooth transmission, and comfortable ride. However, some noted the relatively high fuel consumption and CO2 emissions compared to smaller-engined models. Compared to the ML 320 CDI, the ML 420 CDI offered a significant performance upgrade but at a higher price point. The ML 350, with its gasoline engine, provided a different driving experience, prioritizing responsiveness over low-end torque. The ML 420 CDI appealed to buyers who prioritized power and refinement and were willing to accept the higher running costs associated with a large-displacement diesel engine.
Legacy
The OM 629 engine, while robust, is known to require diligent maintenance, particularly regarding the fuel injection system and turbocharger. The 7G-TRONIC transmission is generally reliable but can be susceptible to issues if not serviced regularly. Today, the ML 420 CDI represents a relatively rare and desirable variant of the W164 M-Class. Well-maintained examples command a premium in the used car market. Its combination of power, luxury, and all-wheel-drive capability continues to appeal to enthusiasts seeking a capable and distinctive SUV. The ML 420 CDI serves as a reminder of a time when large-displacement diesel engines were a viable and popular option in the luxury SUV segment.
