An aluminum body and a fancy eight-speed automatic can get you far in life, not to mention on the open road. But to go for the best fuel economy, big luxury sedans gun for either hybrid drivetrains or diesel engines.
In the 2014 Audi A8, it's the latter that drives its EPA numbers into a whole new realm. The newest addition to the A8 lineup, the TDI, comes with a turbodiesel engine with 240 horsepower and 406 pound-feet of torque. It's the least quick performer of the lineup, but it's the one with the biggest payoff in range. Audi says its A8 L TDI is EPA-rated at 24 miles per gallon city, 36 miles per gallon highway, and 28 miles per gallon combined. We've recently driven one, and saw 35.6 mpg in a 700-mile trip made up of mostly interstate miles.
The TDI complements a pair of engines new for the 2013 model year. Base A8s sport a supercharged 3.0-liter V-6 with stop/start that's rated at 18 mpg city, 28 mpg highway, and 21 mpg combined, while both the short- and long-wheelbase models also can be fitted with a twin-turbo V-8. Short-wheelbase V-8s settle in at 17/28 mpg, or 21 mpg combined, while long-wheelbase sedans are pegged at 16/26 mpg, or 19 mpg combined.
Gas mileage takes a nose dive with the 500-hp, 6.3-liter W-12 engine. As a long-wheelbase model, the A8 L W12 is rated at 13/21 mpg, or 16 mpg combined, figures we'd associate with a large luxury SUV at first glance. That's why you'll see a $2,100 gas-guzzler tariff applied to its sticker, on top of its $134,500 base price.