2013 Mercedes-Benz E350 BlueTEC

When you hear the word "diesel," you probably think of black smoke billowing from a noisy truck or an old Mercedes-Benz from the 1970s. But European automakers have been refining their powerful and fuel-efficient diesel engines for years now, and we're seeing the results of that work in cars like the Mercedes-Benz E-350 BlueTec.

The E-Class sedan uses a 3-liter turbodiesel V6 to produce 210 horsepower and 400 pound-feet of torque. With that much twist it accelerates smartly—though not quite at the the swift pace of gas-powered V8s in the midsize luxury segment. While a slight diesel clatter can be heard outside the car, it is imperceptible inside the well-insulated cabin. Rewards come at the fuel pump, where the E350 BlueTEC returns 21 mpg city and 32 mpg highway.

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A seven-speed automatic transmission comes with standard paddle shifters. As with all E-Class sedans, the BlueTEC's ride is soft but composed, and the interior is as comfortable as it is sophisticated. New features for 2013 include an updated mbrace telematics system and an available Bang & Olufsen sound system.

The new breed of clean diesels hasn't caught on in the United States—perhaps because Americans remember the slow, dirty diesels of decades past. But the polished E350 BlueTEC is sure to make believers out of some.