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Mercedes-Benz SLK250 CDI BlueEfficiency review (2012 onwards)
Model: Mercedes-Benz SLK250 CDI AMG Sport, £36,250 (£43,805 as tested)
Bodystyle: two-door, two-seat, folding-hard top roadster
Engine: 2.1-litre four cylinder twin-turbo diesel, 204hp @ 4,200rpm, 369lb ft @ 1,600rpm
Transmission: seven-speed automatic, rear-wheel drive
Efficiency: 56.5mpg, 132g/km
Performance: 6.7secs 0-62mph, 151mph top speed
What is it?
Perhaps the most intriguing offering in the Mercedes SLK range, the SLK250 CDI BlueEfficiency includes all the usual luxury of the German marque's smallest folding-hard top roadster, but with the added bonus of a 2.1-litre twin-turbocharged diesel engine.
But is it really a bonus? In terms of economy and efficiency, that's a certain yes. According to Mercedes this car is capable of topping 56mpg and returns CO2 emissions of just 132g/km - significantly better than any other rival.
The question is whether this comes at the expense of the rest of the driving experience. Do people actually worry that much about their sports car's mpg? An alluring exhaust note and an invigorating driving experience are surely universal priorities for this kind of machinery.
Can the SLK250 CDI deliver?
Where does it fit?
It looks promising on paper. The 2.1 twin-turbo, already familiar throughout Mercedes' more routine passenger car range, is fitted here in its maximised 204hp state of tune.
This also means 369lb ft of torque - almost as much twisting force as the high performance SLK55 AMG. As if that wasn't impressive enough, the diesel kicks the full mule at just 1,600rpm, whereas the AMG doesn't make its 390lb ft peak until 4,500rpm. Both will spin the rear tyres with ease.
That's at least a second quicker
All told, this gives the SLK250 CDI enough shove to see off 62mph in just 6.7 seconds, and push it all the way to 151mph flat out. That's at least a second quicker over the benchmark sprint than the only premium diesel roadster rival, Audi's 170hp 2.0-litre TDI TT.
If you're looking to compare this to a Porsche Boxster or a BMW Z4 then you'll be picking a petrol alternative. In terms of Mercedes, the SLK is the firm's smallest two-seater, the entry point on a ladder that also includes the Merc SL and the Merc SLS AMG.
Is it for you?
Now in its third generation, the SLK is the original folding-hard top roadster, giving you the security of a coupé and the open-air thrills of a convertible at the whim of a convenient button press. With that Mercedes image it's a classy option, too, and better to drive now than it's ever been.
Rivals like the BMW Z4 have followed the folding-hard top route; others such as the Boxster - and indeed the TT - continue with a fabric soft top design, which is faster to operate, lighter and makes for easier packaging. But can't repel a thug with a knife.
Why pick the diesel? Perhaps because you prefer how diesels deliver their performance - riding along on a wave of torque might just mean more to you than squeezing every last rev out of the redline. Especially if you have nervous passengers. Or maybe you genuinely are interested in supreme economy.
What does it do well?
We'll get onto the fuel consumption in a moment, but the gains here come in addition to a fine selection of existing SLK strengths. Starting with the way it looks every bit the junior SLS these days, and has an interior that will leave all but the most highbrow passengers impressed.
Admittedly, our test car was finished in the fancier AMG Sport trim, and adorned with a substantial number of baubles; basic list price at present is £36,250, while this one was optioned up to £43,805. Yet even taking this into account you can get a lot of luxury for your money.
A very easy car to drive rapidly
The diesel lump makes it a very easy car to drive rapidly, too. Combined with a seven-speed automatic gearbox, passing slower traffic is merely a matter of pressing down harder with your right foot and letting the Mercedes figure out the rest.
Though there are paddles for manual changes, we found the smoothest approach to a twisty road was to simply switch the gearbox to its Sport programme. This does a great job of predicting sensible downshift points, and means one less thing to worry about on the entry to corners.
What doesn't it do well?
The SLK is best approached in the relaxed manner this implies. Driven in such a carefree way - as we suspect the target audience will - it's well judged. The steering is responsive without being overly intimate, the brakes give no cause for complaint and there is plenty of grip rain or shine.
We would probably be even more effusive about its road manners, in fact, if we hadn't just driven the third generation Boxster. Fuel choice issue aside, the Porsche quite frankly knocks the SLK into a proverbial cocked hat as a driver's device - even in terms of more prosaic areas, such as the ride quality.
With the big solid folding roof - weighted further in this case by an optional panoramic glass panel - the SLK is heavy metal, the 250 CDI hitting 1,590kg before options (the Boxster is over 200kg lighter). With 18-inch alloys as well you've got a recipe for quite a bit of crashing and banging around town.
Even with the £1,010 Dynamic Handling Package fitted, which includes continuously variable damping, it never feels light on its feet. It's also hard to ignore how unrefined the 2.1-litre diesel engine is in this car - rattling away at idle speeds and juddering through the start-stop procedure.
What is it like to live with?
That said, once you're running at speed the noise from the diesel becomes less of an issue - the engine itself settles down to a meaningful purr, and you're usually distracted by the rush of the wind past the windscreen once the roof's stowed.
Buffeting in the cabin is minimal with a wind block fitted, and Mercedes still holds the premium monopoly on Airscarf technology. £395 is money well spent when having the car blow hot air on you and your passenger's necks means you can cheerfully spend more time without the lid on.
Travelling with the top down is, after all, the very essence of ownership of this kind of car. Gladly then we're also happy to report it is possible to carry enough luggage for several days away in this mode, and that the SLK250 CDI is ultimately a comfortable and relaxing long distance cruiser.
How green is it?
Mercedes claims 56.5mpg combined for the diesel SLK - which is at least 5mpg better than the Audi TT TDI alternative. The Audi also only achieves 144g/km CO2 at best, compared to 132g/km for the Mercedes.
Ride quality leaves a little to be desired
Some of this difference is accounted for by the TT's quattro four-wheel drive, but there's no escaping the fact that the rear-wheel drive only SLK is also more powerful and faster. It is, however, more expensive as well.
We covered 535 miles during our time with the car, in mixed driving that included motorways, country roads, busy towns and sleepy villages. Despite being enthusiastic wherever possible, according to the trip computer we still averaged 44.8mpg.
Would we buy one?
We can see the appeal - the Mercedes SLK250 CDI is a more than competent cruiser with a good lick of speed when required and class-leading economy. Add in the slick roof, well-appointed cabin and the intrinsic value of the three-pointed star, and it makes a convincing case for itself.
But the refinement and the ride quality leave a little to be desired. And while we didn't miss the exciting exhaust note too much in the end, if you're looking for something that's great to drive, the Boxster leaves the rest of this segment trailing so far behind they can't even see its dust.
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