Mercedes SLK 250 CDI Review: 56.5 MPG Diesel Roadster

The Mercedes SLK 250 CDI marks a bold evolution in the luxury convertible segment, introducing a diesel engine to the iconic SLK lineup for the first time. This model combines the thrill of open-top driving with remarkable fuel efficiency, delivering up to 56.5 mpg in combined cycle testing. Powered by a 2.1-liter turbo diesel producing 204 horsepower and a substantial 369 lb-ft of torque, it accelerates from 0-62 mph in just 6.7 seconds while maintaining a top speed of 151 mph. Ideal for those seeking glamour without compromise on practicality, the SLK 250 CDI stands out against petrol rivals like the Audi TT, offering superior economy at 132 g/km CO2 emissions.

Powertrain and Performance Excellence

At the heart of the SLK 250 CDI lies Mercedes’ proven 2.1-liter four-cylinder diesel engine, refined for roadster duties. It generates 204 bhp from low revs, with peak torque arriving as early as 1,400-1,600 rpm, ensuring effortless overtaking and motorway cruising. Paired exclusively with a seven-speed automatic transmission featuring paddle shifters, the gearbox shifts smoothly in auto mode and responds promptly in sport or manual settings.

Real-world acceleration impresses, with testers noting seamless in-gear punch that makes the car feel quicker than its figures suggest, especially beyond 30 mph. The engine’s stop-start system operates discreetly, restarting without vibration, enhancing urban drivability. Despite its diesel nature, background noise is minimal once warm, often indistinguishable from petrol counterparts with the roof down. At idle or low speeds, some refinement could be better, but on the move, it settles into a refined hum.

Fuel Efficiency and Running Costs

One of the SLK 250 CDI’s standout features is its exceptional fuel economy, officially rated at 56.5 mpg combined – a figure that outpaces most petrol superminis and rivals like the Audi TT’s 53.3 mpg. Independent tests confirm this prowess, with one long-term evaluation achieving 51.3 mpg over 1,000 miles of mixed driving, and another hitting 42 mpg during spirited A-road runs. Enthusiastic driving drops figures to the mid-30s, but steady motorway use easily exceeds 50 mpg.

CO2 emissions of 132 g/km place it in a lower tax bracket, and its diesel particulate filter (DPF) ensures compliance with emissions standards. Priced from around £36,250, it’s notably cheaper than the equivalent petrol SLK 250 by over £2,000, amplifying savings on fuel and road tax. Insurance falls into group 20, making it accessible for premium convertibles. Kerb weight of 1,590 kg aids efficiency without sacrificing presence.

• Official MPG: 56.5 combined, beating petrol SLK by 13 mpg
• Real-World: 42-51 mpg depending on conditions
• Emissions: 132 g/km CO2
• Price Advantage: Lower entry cost than petrol variants

Chassis Dynamics and Ride Comfort

The SLK 250 CDI excels in delivering a planted, composed ride suited to grand touring rather than track-day aggression. Its sports suspension and low-profile tires handle undulations adeptly, providing comfort on long journeys while remaining responsive through corners. Motorway stability is exemplary, with minimal wind noise even at high speeds and the fabric roof up.

Handling is tidy and predictable, though it prioritizes luxury over razor-sharp sportiness. The chassis feels balanced, but enthusiastic driving lacks the raw fun of lighter petrol roadsters. Steering is precise yet weighted for relaxed cruising, and the diesel’s low-end torque enhances mid-corner confidence without needing frequent gear changes. Ride quality surprises with its damping, absorbing bumps effectively despite the firm setup.

Retractable Hardtop and Practicality

Mercedes’ signature retractable hardtop operates in 18 seconds at speeds up to 30 mph, transforming the SLK from coupe to cabriolet seamlessly. Constructed from lightweight metal, it maintains structural rigidity and excellent noise insulation. However, it consumes significant boot space – around 210 liters with the roof stowed – limiting luggage to smaller items; care is needed to avoid crushing gear during operation.

Front seats offer ample support with adjustable lumbar settings, accommodating taller drivers comfortably. Rear space is predictably absent, but this two-seater prioritizes couple-friendly dimensions. Visibility remains good, aided by parking sensors standard on most trims.

Interior Refinement and Technology

Inside, the SLK 250 CDI exudes Mercedes quality with leather upholstery, climate control, and an intuitive COMAND infotainment system featuring sat-nav and Bluetooth. Build materials feel premium, and the cockpit layout focuses the driver with a high cowl and optional sports seats. Ambient noise is low, especially with the acoustic roof and optional wind deflector.

Standard kit on AMG Sport models includes xenon lights, 18-inch alloys, and stability control. Higher trims add keyless entry and adaptive cruise. While not the most modern by today’s standards, the tech delivers reliably for its era.

Safety and Reliability Features

Safety is robust, with seven airbags, electronic stability program, and attention assist monitoring driver fatigue. The diesel’s DPF and BlueEfficiency tech minimize environmental impact. Mercedes’ reputation for durability shines, with main-dealer servicing ensuring longevity; low-mileage examples remain in excellent condition.

Market Position and Rivals

The SLK 250 CDI slots between petrol hot hatches and pure sports cars, appealing to efficiency-focused luxury buyers. It trumps the Audi TT Diesel in mpg and torque, while offering Mercedes badge prestige over BMW Z4 equivalents (which lacked diesel at the time). For diesel convertible fans, few match its blend of glamour and frugality.

Pros and Cons Overview

• Pros: Outstanding fuel economy, strong low-end torque, refined highway cruiser, premium interior, value pricing
• Cons: Boot space limited by roof mechanism, diesel clatter at idle, less playful handling than petrol rivals

Who Should Buy the SLK 250 CDI?

This roadster suits executives desiring stylish, efficient open-top motoring for weekends and commutes. It’s perfect for long-distance travelers prioritizing comfort and low running costs over outright sportiness. Budget-conscious buyers will appreciate its petrol-beating economy in a luxury package.

Frequently Asked Questions (FAQs)

Is the SLK 250 CDI reliable?

Yes, Mercedes diesels are durable, with proper maintenance via main dealers ensuring trouble-free ownership.

How does the fuel economy compare in real life?

Expect 42-51 mpg mixed, up to 56 mpg on motorways.

Can the roof operate while driving?

Up to 30 mph, in about 18 seconds.

What’s the boot space like?

210 liters roof up; reduced with roof down.

Is it fun to drive?

Capable and torquey, but more GT than track-focused.