COMBINING the words ‘diesel’ and ‘sports car’ is not quite a new concept, but when you make the sports car a luxury rear-wheel-drive model famed for its looks and road manners it takes on new significance.
Most diesel sports cars are actually just front-wheel-drive coupes based on fairly ordinary hatchbacks, and as such the architecture is ready-plumbed for diesels. Customers want high MPG figures and diesel gives that to them, and the sales figures show that MPG is a higher priority for many than driving pleasure.
Let’s be honest; there are (very) few diesel cars out there that are fun to drive, but rear-wheel-drive is all about driving pleasure and the SLK is a relatively affordable luxury sports car platform with a healthy bundle of likeable traits behind the wheel.
That’s why putting an oil-burner under its bonnet is a big deal. The engine in question is a familiar ‘250’ designated four-cylinder CDI unit pinched from the C-Class, pushing out over 200bhp and a torque curve that would embarrass a naturally-aspirated petrol V6. Outright performance isn’t really an issue.
The choice of a four-pot diesel instead of a V6 means the SLK CDI’s front end has been kept light enough to maintain that lovely direct, darting agility at the front wheels. Then there’s the range. A mix of mostly motorway mileage and a smattering of town driving left a gnat’s wing under half a tank left – but by then I’d already covered 500 miles.
That huge potential range is one of the CDI model’s big selling points. If you’re driving to the Alps you’ll spend a lot less getting there in this than you would in, say, an SLK 350 petrol.
It maintains all the existing SLK features, including the folding electric hard top roof, which isn’t the fastest around but makes a decent fist of noise insulation when it’s up.
As with all Mercedes cars the options list is deep should you wish to plunder it, and the test car was fitted with heated leather seats among other niceties. Mercedes’ materials quality is generally sublime. The ‘Airscarf’ warm air vents behind your neck are another nice touch.
It rides well too, even on the large and rather striking five-spoke AMG alloy wheels. The engine doesn’t upset the balance in any perceptible way. But even though it does have good things going for it, in other ways it’s heavily compromised.
True sports cars are all about passion; about technical excellence and communication with the driver to create driving enjoyment. Part of that is throttle response – you want the engine to respond the instant you breathe on the accelerator pedal, and the SLK 250 CDI just doesn’t.
The reality is that despite clever turbocharging technology you have to give the pedal a concerted mash before any forward thrust appears. It makes powering out of roundabouts and attempting to find a rhythm along a country road far more frustrating than it should be. It feels slower-witted than a petrol SLK.
It isn’t progressive enough either; it delivers a big thump of torque and then tails off a little towards 4,000rpm, so it doesn’t behave like a sports car should when you drive up the revs and up through the gears. It behaves, well, like a diesel C-Class.
Nor is it especially quiet. Mercedes’ V6 diesels are among the very best, but this four-cylinder unit is a bit uncouth and noisy for a convertible. The SLK just isn’t a good fit for the diesel if either outright luxury or Sunday afternoon blasts are your thing.
On the face of it, it presents a bit of a marketing problem for Mercedes because the SLK itself and the 250 CDI engine represent different ideals. The SLK’s stunning looks – and there are few other cars for the price that turn more heads – say something entirely different to the technologically advanced, efficient but noisy and mismatched engine… but then there’s a reality check.
In these times the number of people who want something that looks great but costs less to fuel is growing like a magic bean in Miracle-Gro. Generally speaking the number of people who really care how a car drives is going down, and the number who’d just prefer to visit filling stations less often is going up. And to the latter group, the SLK CDI is absolutely superb. Frankly it almost markets itself.
If you want rear-wheel-drive thrills with cheaper fuel bills, this isn’t the place to look. If you want top-drawer style, excellent comfort and potentially huge range without worrying about all that sports car malarkey, this is the one for you.
FACTS AT A GLANCE
Model: Mercedes-Benz SLK 250 CDI, £36,250 on the road.Engine: 2.1-litre turbocharged four-cylinder diesel producing 201bhp and 369lb.ft.Transmission: 7-speed automatic gearbox driving the rear wheels.Performance: Top speed 151mph, 0-62mph in 6.7 seconds.Fuel economy: 56.5mpg.CO2 rating: 132g/km.