After a lunch of bruschetta, pizza, and gelato, which is an ironic way to fuel up for testing a German car, Mercedes-Benz product manager Bart Herring gets straight to boasting. "No one is better positioned to bring diesel models to the market," he says. "Diesel is very well suited to what people want." Even setting aside Herring's praise, the new 2013 Mercedes-Benz GLK250 BlueTec 4Matic is clearly something unique. Not only is it America's only diesel compact crossover, it also handily tops its segment in fuel economy. The 2013 Mercedes-Benz GLK250 returns 24/33 mpg (city/highway), giving a cruising range of 515 miles per tank. The existing GLK350, which has a 302-hp gasoline V-6, manages just 19/24 mpg with all-wheel drive. No other compact luxury crossover comes close to the BlueTec's ratings, even those with thrifty 2.0-liter turbo-four gas engines like the Audi Q5, the BMW X3, and the Range Rover Evoque. None of those competitors can crack 21 mpg in the city and 28 mpg on the highway when fitted with all-wheel drive. Only hybrids come close: the Q5 hybrid returns 24/30 mpg, yet it's $12,300 more expensive than the Mercedes, while the Lexus RX450h manages 30/28 mpg but costs $9110 more. In other words, the GLK250 offers a lot of fuel-economy bang for the buck. The GLK250 BlueTec uses a 2.1-liter, twin-turbocharged four-cylinder diesel engine codenamed OM651. The twin-turbo setup is designed to increase responsiveness: a large turbo helps provide maximum power, while a smaller one spools up quickly to reduce lag in low-load conditions. The engine computer opens and closes a bypass valve so that the large turbo is only used at higher speeds when more boost is needed. Peak torque of 369 lb-ft is available from just 1600 rpm. An AdBlue injection system cleans up the exhaust so the GLK meets particulate-emissions requirements in all 50 states. In Europe, this engine gets an automatic stop/start feature to save more fuel, but it's not installed on the U.S. version. Peter Lückert, director of diesel powertrain development, says stop/start doesn't help U.S. fuel-economy test results, and American drivers are less interested in the technology than are Europeans. The 2.1-liter diesel is also used here in the Sprinter cargo van and will launch in the E250 BlueTec sedan this September. Around town, the GLK250 moves off the line just as easily as a comparable SUV with a gasoline turbo-four engine. The accelerator has the precise, progressive tip-in of other Mercedes products, and there is barely any turbo lag. Most drivers will never suffer the wait-wait-wait- power delivery long associated with diesel engines; only if you floor the accelerator from a stop is a second of lethargy evident.