The testing of 2012′s Mercedes SLK took a turn for the worst, when smoke started billowing from under its hood. The vehicle broke down during a trial run around Germany’s Nürburgring track. According to the internets: “It is speculated that for the first time in its history the SLK will also be offered with a turbo diesel engine.” Maybe it needs a little more fine tuning. Thanks to World Car Fans for the spy shots!