The Mercedes-Benz M-Class (W164) ML 420 CDI 4MATIC, produced from 2008 to 2009, was a high-performance variant within the second-generation M-Class range. It served as a bridge between the more accessible ML 320 CDI and the flagship ML 550, appealing to buyers who desired a blend of luxury, power, and substantial towing capability. This model combined a potent V8 diesel engine with Mercedes-Benz’s 7G-TRONIC automatic transmission and the 4MATIC all-wheel-drive system. The W164 facelift, introduced in 2008, brought with it styling refinements and technological upgrades across the entire M-Class lineup, including the ML 420 CDI.
Technical Specifications
| Brand | Mercedes-Benz |
| Model | M-Class |
| Generation | M-Class (W164, facelift 2008) |
| Type (Engine) | ML 420 CDI V8 (306 Hp) 4MATIC 7G-TRONIC |
| Start of production | 2008 |
| End of production | 2009 |
| Powertrain Architecture | Internal Combustion engine |
| Body type | SUV |
| Seats | 5 |
| Doors | 5 |
| Fuel consumption (urban) | 14.2-14.6 l/100 km (16.6 – 16.1 US mpg, 19.9 – 19.3 UK mpg, 7 – 6.8 km/l) |
| Fuel consumption (extra urban) | 8.5-9.1 l/100 km (27.7 – 25.8 US mpg, 33.2 – 31 UK mpg, 11.8 – 11 km/l) |
| Fuel consumption (combined) | 10.6-11 l/100 km (22.2 – 21.4 US mpg, 26.6 – 25.7 UK mpg, 9.4 – 9.1 km/l) |
| CO2 emissions | 279-292 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 | 235 km/h (146.02 mph) |
| Emission standard | Euro 4 |
| Weight-to-power ratio | 7.3 kg/Hp, 136.6 Hp/tonne |
| Weight-to-torque ratio | 3.2 kg/Nm, 312.5 Nm/tonne |
| Power | 306 Hp @ 3600 rpm |
| Torque | 700 Nm @ 2000-2600 rpm (516.29 lb.-ft. @ 2000-2600 rpm) |
| Engine layout | Front, Longitudinal |
| Engine Model/Code | OM 629.912 |
| Engine displacement | 3996 cm3 (243.85 cu. in.) |
| Number of cylinders | 8 |
| Engine configuration | V-engine |
| Cylinder Bore | 86 mm (3.39 in.) |
| Piston Stroke | 86 mm (3.39 in.) |
| Compression ratio | 17:1 |
| Number of valves per cylinder | 4 |
| Fuel injection system | Diesel Commonrail |
| Engine aspiration | BiTurbo, Intercooler |
| Valvetrain | DOHC |
| Engine oil capacity | 11.5 l (12.15 US qt | 10.12 UK qt) |
| Coolant | 12 l (12.68 US qt | 10.56 UK qt) |
| Kerb Weight | 2240 kg (4938.35 lbs.) |
| Max. weight | 2950 kg (6503.64 lbs.) |
| Max load | 710 kg (1565.28 lbs.) |
| Trunk (boot) space – minimum | 833 l (29.42 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) |
| Max. roof load | 100 kg (220.46 lbs.) |
| Permitted trailer load with brakes (12%) | 3500 kg (7716.18 lbs.) |
| Permitted trailer load without brakes | 750 kg (1653.47 lbs.) |
| Length | 4781 mm (188.23 in.) |
| Width | 1911 mm (75.24 in.) |
| Width including mirrors | 2124 mm (83.62 in.) |
| Height | 1815 mm (71.46 in.) |
| Wheelbase | 2915 mm (114.76 in.) |
| Front track | 1636 mm (64.41 in.) |
| Rear track | 1639 mm (64.53 in.) |
| Front overhang | 866 mm (34.09 in.) |
| Rear overhang | 1000 mm (39.37 in.) |
| Ride height (ground clearance) | 186-261 mm (7.32 – 10.28 in.) |
| Drag coefficient (Cd) | 0.37 |
| Minimum turning circle | 11.6 m (38.06 ft.) |
| Approach angle | 25-31° |
| Departure angle | 24-29° |
| Ramp-over angle | 14-21° |
| Climb angle | 45° |
| Wading depth | 500 mm (19.69 in.) |
| Drivetrain Architecture | The Internal combustion engine (ICE) drives permanently the four wheels of the vehicle. |
| Drive wheel | All wheel drive (4×4) |
| Number of gears and type of gearbox | 7 gears, automatic transmission G-TRONIC |
| Front suspension | Double wishbone, Transverse stabilizer, Air suspension |
| Rear suspension | Independent multi-link suspension, Air suspension, Transverse stabilizer |
| Front brakes | Ventilated discs |
| Rear brakes | Disc |
| Assisting systems | ABS (Anti-lock braking system) |
| Steering type | Steering rack and pinion |
| Power steering | Hydraulic Steering |
| Tires size (Front) | 255/50 R19; 265/45 R20; 265/40 R21 |
| Tires size (Rear) | 255/50 R19; 285/45 R19; 265/45 R20; 265/40 R21 |
| Wheel rims size (Front) | 8J x 19; 8.5J x 19; 8.5J x 20; 9J x 21 |
| Wheel rims size (Rear) | 8J x 19; 9.5J x 19; 8.5J x 20; 9J x 21 |
Powertrain & Engine Architecture
The ML 420 CDI was powered by the OM 629.912, a 4.0-liter V8 diesel engine. This engine utilized a common rail direct injection system, delivering fuel at extremely high pressures for optimized combustion. The engine featured twin turbochargers with an intercooler, boosting power and torque output. The valvetrain employed three valves per cylinder (two intake, one exhaust) and a double overhead camshaft (DOHC) design. The 7G-TRONIC automatic transmission, a seven-speed unit, was specifically tuned to handle the engine’s substantial torque. This transmission offered smooth shifts and contributed to improved fuel efficiency compared to older automatic designs. The transmission’s gear ratios were optimized for both acceleration and highway cruising.
Driving Characteristics
The ML 420 CDI offered a distinctly different driving experience compared to its gasoline-powered siblings. The high torque output of the diesel engine, available from a low 2000 rpm, provided effortless acceleration and strong pulling power, making it an excellent choice for towing. While not as rev-happy as the ML 550, the ML 420 CDI delivered a more relaxed and confident driving experience, particularly on the highway. The 7G-TRONIC transmission contributed to smooth gear changes, and the 4MATIC all-wheel-drive system provided enhanced traction in various weather conditions. The air suspension, standard on this model, offered a comfortable ride quality, absorbing bumps and irregularities in the road surface effectively.
Equipment & Trim Levels
The ML 420 CDI typically came well-equipped with standard features including leather upholstery, power-adjustable front seats with memory function, dual-zone automatic climate control, a premium audio system, and parking sensors. Optional extras included a navigation system, rear-seat entertainment system, panoramic sunroof, and upgraded interior trim options. The overall interior design emphasized luxury and comfort, with high-quality materials and a refined aesthetic.
Chassis & Braking
The W164 M-Class featured a robust chassis designed to handle the weight and power of the V8 engine. The front suspension utilized a double wishbone setup with a transverse stabilizer bar, while the rear suspension employed an independent multi-link design, also with a stabilizer bar. Air suspension was standard, providing adjustable ride height and improved comfort. The braking system consisted of ventilated discs at all four corners, coupled with ABS (Anti-lock Braking System) for enhanced stopping power and control.
Market Reception & Comparison
The ML 420 CDI was generally well-received by automotive critics, who praised its powerful engine, comfortable ride, and luxurious interior. However, some reviewers noted the engine could be somewhat noisy compared to gasoline engines, a common characteristic of diesel powerplants. Compared to the ML 320 CDI, the ML 420 CDI offered significantly more power and performance. Against the ML 550, it provided a more fuel-efficient alternative, albeit with slightly less overall horsepower. Fuel economy was a strong point, offering better mileage than the gasoline-powered models, especially on long journeys.
Legacy
The OM 629 engine family, including the 629.912 found in the ML 420 CDI, is known for its durability and longevity when properly maintained. While diesel engines generally require diligent maintenance, including regular oil changes and fuel filter replacements, these engines can accumulate high mileage without major issues. In the used car market, the ML 420 CDI remains a desirable option for buyers seeking a capable and luxurious SUV with strong towing capacity. However, potential buyers should be aware of the higher maintenance costs associated with diesel engines and the potential for issues with the emissions control systems as the vehicle ages.
