The Mercedes-Benz SLK (R172) SLK 250 CDI: A Diesel Roadster with Unexpected Flair
The Mercedes-Benz SLK (R172) represents the third generation of the German automaker’s compact luxury roadster, a vehicle segment designed to offer open-top driving pleasure combined with premium appointments and the prestige of the three-pointed star. Produced from 2012 to 2015, the R172 generation brought a more assertive design language, enhanced technology, and a refined driving experience. Among its diverse powertrain offerings, the SLK 250 CDI stood out, particularly within European markets, for its blend of robust performance and exceptional fuel efficiency, a somewhat unconventional pairing for a two-seat convertible. This variant, equipped with the 7G-TRONIC PLUS automatic transmission, showcased Mercedes-Benz’s engineering prowess in delivering a compelling diesel-powered luxury roadster.
Engine and Performance of the Mercedes-Benz SLK (R172) SLK 250 CDI
At the heart of the Mercedes-Benz SLK (R172) SLK 250 CDI lies Mercedes-Benz’s acclaimed OM 651.980 engine, a 2.1-liter (2143 cm3 or 130.77 cu. in.) inline-four turbodiesel powerplant. This sophisticated unit is a testament to modern diesel engineering, featuring a twin-turbo setup and common rail direct fuel injection, along with a DOHC (Dual Overhead Camshaft) valvetrain with four valves per cylinder. This configuration allows the engine to produce a potent 204 horsepower at 3800 rpm, translating to a remarkable 95.2 horsepower per liter. However, the true highlight of this diesel engine is its prodigious torque output: a commanding 368.78 lb.-ft. (500 Nm), available across a broad and accessible rev range from 1600 to 1800 rpm.
This substantial torque, delivered early in the rev band, provides the SLK 250 CDI with impressive real-world responsiveness and effortless acceleration. Coupled with Mercedes-Benz’s smooth and efficient 7G-TRONIC PLUS seven-speed automatic transmission, the roadster can sprint from 0 to 60 mph in a brisk 6.4 seconds, with a top speed electronically limited to approximately 151 mph (243 km/h). The engine’s front, longitudinal layout and rear-wheel-drive architecture ensure a classic sports car feel, while its advanced systems, including a Start & Stop System and a Particulate filter, contribute to its Euro 5 emission standard compliance and overall efficiency.
Perhaps the most compelling aspect of the SLK 250 CDI’s performance is its fuel economy. For a luxury roadster capable of spirited driving, its consumption figures are outstanding: an estimated 48 US mpg combined (4.9-5 l/100 km). Even in urban driving, it achieves an impressive 37.9-38.6 US mpg, extending to 54.7-57.4 US mpg on the highway. This remarkable efficiency, combined with a 15.85 US gallon (60 liter) fuel tank, granted the SLK 250 CDI an exceptional cruising range, making it an ideal choice for long-distance European touring.
Design and Features
The R172 generation of the SLK marked a significant evolution in design, drawing inspiration from the iconic Mercedes-Benz SLS AMG. Its more aggressive, upright grille, swept-back headlights, and muscular fender lines gave the Mercedes-Benz SLK (R172) a more mature and commanding presence compared to its predecessors. As a classic roadster, it features a sleek, two-door, two-seat body type, emphasizing its pure driving focus. A signature feature of the SLK, retained and refined in the R172, is its innovative “Vario-Roof” – a retractable hardtop that seamlessly transforms the car from an elegant coupe to an open-air roadster in mere seconds. This provides the best of both worlds: the security and refinement of a fixed roof and the exhilarating experience of top-down motoring.
Inside, the SLK 250 CDI offered a cabin that blended sportiness with luxury. High-quality materials, meticulous craftsmanship, and ergonomic design were hallmarks. Features like the optional AIRSCARF system, which delivers warm air to the occupants’ necks, enhanced comfort during cooler open-top drives. Standard equipment included power-adjustable seating, a sophisticated infotainment system, and a suite of Mercedes-Benz’s renowned safety technologies. The instrument panel was driver-focused, with clear gauges and intuitive controls. Despite its compact dimensions, the SLK offered practical trunk space ranging from 7.95 cu. ft. (225 liters) with the top down to 11.83 cu. ft. (335 liters) with the top up, accommodating weekend getaways.
Underneath its stylish skin, the SLK 250 CDI featured a robust chassis designed for both comfort and dynamic handling. The front suspension utilized an independent McPherson strut setup with coil springs and an anti-roll bar, while the rear employed an independent multi-link spring suspension with a stabilizer. Ventilated disc brakes up front and solid discs at the rear, coupled with ABS (Anti-lock Braking System), provided confident stopping power. The hydraulic rack-and-pinion power steering offered precise feedback, ensuring an engaging driving experience. Standard tire sizes were 205/55 R16 on 7J x 16 wheels, contributing to a balanced ride and handling profile.
Technical Specifications: Mercedes-Benz SLK (R172) SLK 250 CDI (204 Hp) 7G-TRONIC PLUS
| Category | Specification |
|---|---|
| General Information | |
| Brand | Mercedes-Benz |
| Model | SLK |
| Generation | SLK (R172) |
| Type (Engine) | SLK 250 CDI (204 Hp) 7G-TRONIC PLUS |
| Start of Production | 2012 year |
| End of Production | 2015 year |
| Powertrain Architecture | Internal Combustion engine |
| Body type | Roadster |
| Seats | 2 |
| Doors | 2 |
| Performance Specs | |
| Fuel Consumption (Urban) | 6.1-6.2 l/100 km (37.9-38.6 US mpg) |
| Fuel Consumption (Extra Urban) | 4.1-4.3 l/100 km (54.7-57.4 US mpg) |
| Fuel Consumption (Combined) | 4.9-5 l/100 km (47-48 US mpg) |
| CO2 Emissions | 128-132 g/km |
| Fuel Type | Diesel |
| Acceleration 0 – 60 mph | 6.4 sec |
| Acceleration 0 – 62 mph (0-100 km/h) | 6.7 sec |
| Maximum Speed | 150.99 mph (243 km/h) |
| Emission Standard | Euro 5 |
| Weight-to-Power Ratio | 7.4 kg/Hp, 134.7 Hp/tonne |
| Weight-to-Torque Ratio | 3 kg/Nm, 330 Nm/tonne |
| Engine Specs | |
| Power | 204 Hp @ 3800 rpm |
| Power per liter | 95.2 Hp/l |
| Torque | 368.78 lb.-ft. (500 Nm) @ 1600-1800 rpm |
| Engine Layout | Front, Longitudinal |
| Engine Model/Code | OM 651.980 |
| Engine Displacement | 2143 cm3 (2.1 L / 130.77 cu. in.) |
| Number of Cylinders | 4 |
| Engine Configuration | Inline |
| Cylinder Bore | 3.27 in. (83 mm) |
| Piston Stroke | 3.9 in. (99 mm) |
| Compression Ratio | 16.2:1 |
| Number of Valves per Cylinder | 4 |
| Fuel Injection System | Diesel Commonrail |
| Engine Aspiration | Twin-Turbo, Intercooler |
| Valvetrain | DOHC |
| Engine Oil Capacity | 6.87 US qt (6.5 l) |
| Coolant Capacity | 10.14 US qt (9.6 l) |
| Engine Systems | Start & Stop System, Particulate filter |
| Space, Volume and Weights | |
| Kerb Weight | 3340 lbs. (1515 kg) |
| Max. Weight | 4199.81 lbs. (1905 kg) |
| Max Load | 859.8 lbs. (390 kg) |
| Trunk (boot) space – Minimum | 7.95 cu. ft. (225 l) |
| Trunk (boot) space – Maximum | 11.83 cu. ft. (335 l) |
| Fuel Tank Capacity | 15.85 US gal (60 l) |
| Dimensions | |
| Length | 162.76 in. (4134 mm) |
| Width | 71.26 in. (1810 mm) |
| Width Including Mirrors | 78.98 in. (2006 mm) |
| Height | 51.22 in. (1301 mm) |
| Wheelbase | 95.67 in. (2430 mm) |
| Front Track | 61.38 in. (1559 mm) |
| Rear Track | 61.61 in. (1565 mm) |
| Front Overhang | 34.25 in. (870 mm) |
| Rear Overhang | 32.83 in. (834 mm) |
| Drag Coefficient (Cd) | 0.30 |
| Minimum Turning Circle | 34.51 ft. (10.52 m) |
| Drivetrain, Brakes and Suspension Specs | |
| Drivetrain Architecture | Rear-wheel drive |
| Drive Wheel | Rear wheel drive |
| Number of Gears and Type of Gearbox | 7 gears, automatic transmission G-TRONIC PLUS |
| Front Suspension | Independent, type McPherson with coil spring and anti-roll bar |
| Rear Suspension | Independent multi-link spring suspension with 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 | 205/55 R16 |
| Wheel Rims Size | 7J x 16 |
Legacy and Market Impact
The Mercedes-Benz SLK (R172) SLK 250 CDI occupied a unique niche within the compact luxury roadster segment. While the SLK line itself was a strong competitor to vehicles like the BMW Z4, Audi TT Roadster, and Porsche Boxster, the diesel variant specifically carved out its own space. In markets like the United States, diesel-powered passenger cars, particularly sports cars, have historically been less common due to fuel availability, emissions regulations, and consumer preferences. However, in Europe, where diesel technology is more widely embraced for its efficiency and torque characteristics, the SLK 250 CDI was a compelling proposition.
Its reputation was built on offering a blend of exhilarating open-top motoring with the practical benefits of a diesel engine: lower running costs, impressive range, and abundant low-end torque for effortless cruising and overtaking. This made it a particularly attractive option for drivers who desired a stylish, premium convertible for daily commuting or extensive road trips across the continent, without sacrificing performance. Critics often praised the SLK 250 CDI for its refined powertrain, which, despite being a diesel, delivered smooth power delivery and surprisingly quiet operation for its class.
The R172 generation, and the SLK 250 CDI within it, contributed to Mercedes-Benz’s strategy of diversifying its powertrain offerings to meet varying global market demands and environmental standards. It demonstrated that a diesel engine could be integrated into a luxury roadster without compromising its sporty appeal or premium feel. The SLK (R172) ultimately paved the way for its successor, the SLC-Class, which continued to evolve the compact roadster concept. Today, the SLK 250 CDI remains a testament to Mercedes-Benz’s innovative engineering, offering a distinctive blend of performance, luxury, and efficiency that stands out in the history of modern roadsters.
