According to most purists, a BMW sports coupe or convertible are supposed to have a smooth gasoline engine –preferably an inline-six- mounted up front and sending power to the wheels at the back.
The new 640d xDrive Coupe and Convertible that will debut at the Geneva Motor Show next month ticks only one of those boxes: the straight-six found under the hood. However, it's not fed by gasoline but by diesel fuel and it channels power to all four wheels.
It's not the first diesel-powered 6-Series as that taboo was broken by the previous generation model, but it's the first to combine an oil-burner with BMW's electronically controlled all-wheel drive system.
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