Despite the popularity of large, diesel-powered luxury sedans on the other side of the Atlantic, the segment exists in the current U.S. market thanks only to the Audi A8, which gained a 3.0-liter TDI V-6 option for 2014 to go along with its boosted gasoline powerplants. (Mercedes-Benz previously offered a diesel in the S-class but has yet to introduce one in the latest model.) Starting in 2015, however, BMW wants a slice of the A8 TDI Quattro’s tiny pie and is finally offering its silken inline-six oil-burner in the aging 7-series sedan, which has changed little since its last full redesign in 2009.
A SOLID PLAYER
Similar to the compression-ignition heart of the X5 xDrive35d crossover, the 740Ld’s turbocharged 3.0-liter six is rated at 255 horsepower and a hearty 413 lb-ft of torque at 1500 rpm. The ubiquitous ZF eight-speed automatic is the lone transmission choice, and the diesel is available only with xDrive all-wheel drive and the stretched, 126.4-inch wheelbase of the L model. It’s a lovely engine, pulling smoothly through its limited power band and working well with the gearbox to minimize turbo lag. With only a subtle clatter at idle, this is a far smoother mill than the 2.0-liter diesel four in our long-term 328d xDrive wagon.
The 740Ld’s stats compare favorably with the all-wheel-drive A8 TDI’s, which churns out 240 horsepower and 428 lb-ft and shares the same eight-speed autobox, albeit with its own programming. The aluminum-intensive Audi does have a 130-pound weight advantage over the Bimmer, which bends the scales at a hefty 4715 pounds.
Performance bragging rights go to the 740Ld, however, with it edging out the A8 TDI by a couple of tenths both to 60 mph (6.2 seconds) and through the quarter-mile (14.8 at 93 mph). Lateral grip around the skidpad is a respectable 0.89 g, and our test car came to a halt from 70 mph in just 159 feet on its 20-inch Pirelli P Zero run-flat summer tires. But this is still a committed luxury car and the diesel feels lazy compared with livelier gasoline engines, so it’s best savored at a relaxed pace. The 740Ld’s other primary competitor—BMW’s own 315-hp 740Li xDrive gas-burner—is lighter and more than a half-second quicker in straight-line acceleration.
THE REAL DIFFERENCE
Excellent fuel economy is the diesel’s main selling point, of course, and our test car’s 27-mpg observed average in mixed driving handily beats the 19 mpg we achieved in its gas-fueled sibling. That works out to a 570-mile range with the car’s 21-gallon fuel tank. The 740Ld, however, couldn’t match the A8 TDI’s frugalness, which returned a stellar 32 mpg in our testing. Even though the big Bimmer manages its bulk notably well, it similarly lacks the poise and agility of the lighter Audi on a twisty road, as well as the A8’s exquisite interior trappings and intuitive infotainment and driver interfaces.
The big 7 remains a very luxurious place to sit and cruise, however, with excellent seats up front and tons of room to stretch out in back; highway miles and gridlock frustrations melt away. The design may be showing its age next to the A8’s executive-jet cockpit, but the 7-series has gained a new gauge cluster with a large, configurable TFT display that changes with the car’s various driving modes (Eco Pro, Comfort+, Sport, and Sport+).
THAT’S THE TICKET
The $1500 premium for the 740Ld xDrive (base price $83,450) over its gasoline counterpart is a modest amount, but that sum will take considerably longer to recoup in fuel savings as long as current diesel prices in the U.S. remain higher than gasoline’s. (At this writing, diesel averages 57 cents per gallon higher than regular unleaded.) The other reality is that diesel pumps are still less plentiful in America and are oftentimes grungy and neglected when available.
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