Review: 2010 Mercedes-Benz S400 Hybrid

Up Front

The hybridization of high-end German luxury cars is under way. Daimler (DAI) kicked off the trend with the 2010 Mercedes S400, the gasoline-electric version of its top-of-the-line S-Class sedan. BMW (BMW:GR) has countered with its new, performance-oriented 2011 ActiveHybrid 7. In March, Audi (VOW:GR) showed off a hybrid A8 concept car at the Geneva Auto Show, and Porsche has promised a hybrid version of its new four-door Panamera next year.

Where does the Mercedes-Benz S400 fit in? Basically, it's a hybrid for people who don't want a hybrid, with new technology so seamlessly integrated into the design that you barely know it's there. Mercedes' first hybrid model, it's also the first production car to use lithium-ion batteries, which are small enough to fit into the engine compartment. As a result, the S400 has the same roomy interior and large trunk as a regular S-Class sedan. Trunk space is 16.4 cu. ft., more than in the Lexus LS 600h L (10.1 cu. ft.) and BMW ActiveHybrid 7 (14 cu. ft.).

The S400's other big innovation is its price: Most hybrids carry a premium over conventional gasoline-powered models, but the S400 starts at $88,825, $3,650 less than the least expensive V8-powered Mercedes S-Class sedan, the S550. That makes the S400 the least expensive S-Class sedan sold in the U.S., with a starting price far lower than those of the LS 600h L ($109,675) and the ActiveHybrid 7 ($103,175). (One concern about the Lexus: The LS 600h L has been the subject of two recent recalls, the most recent in early July for an engine valve glitch.)

The S400 is a so-called "mild" hybrid. Its power plant consists of a 3.5-liter, 275-horsepower V6 gasoline engine augmented by a 20-hp electric motor. Small as it is, the disc-shaped electric motor generates 118 lb.-ft. of torque that kicks in instantly when you punch the gas. The combined system generates 295 hp of power and an impressive 284 lb.-ft. of torque. The S400 isn't blazingly fast, but has more than adequate oomph for such a big vehicle.

The S400's electric motor is positioned between the gasoline engine and the seven-speed automatic transmission. The battery pack stores energy collected from a regenerative braking system. To further conserve energy, the gasoline engine shuts off at speeds of less than 9 mph, as well as during idling. At a stoplight, the air-conditioner compressor and power steering pump operate electrically.

The Environmental Protection Agency rates the S400 to get 19 miles per gallon in the city and 25 on the highway, for an average of 21 mpg. That's 27 percent better in city driving and 17 percent better overall than the rear-wheel-drive Mercedes S550, which is rated to get 15/23, for an average of 18. The S400 more or less matches the fuel economy rating of the LS 600h L (20/22 for an average of 21 mpg), and does a tad better than the ActiveHybrid 7 (17/26 for an average of 20 mpg).

However, I suspect many S400 drivers will achieve better than the rated mileage. I got 24 mpg in my test car over 512 miles of mixed driving, during which I made absolutely no effort to conserve fuel. Less lead-footed drivers will probably average 26 or 27 mpg.

S-Class sales are booming this year, at least by comparison with calamitous 2009. U.S. sales more than doubled in June vs. the same month in 2009, to 1,549, and were up 27.2 percent, to 6,405, during the first six months of this year. The S400 is a niche product, with only 524 sold in the U.S. during the first six months of the year, a mere 8.2 percent of total S-Class sales during the period. However, the S400 will seem a lot more attractive when gasoline prices rise again.

Behind the Wheel

What do you give up in opting for the S400 over a conventional model? Quickness, mainly. Mercedes says the S400 will accelerate from zero to 60 in 7.2 seconds, which is plenty fast for most luxury-car drivers. But that's nearly two seconds slower than the S550 (5.4 seconds) and the Lexus LS 600h L (5.5 seconds), and way behind the BMW ActiveHybrid 7 (4.7 seconds).

In other respects, the S400 drives similarly to any S-Class sedan, with less road feel and a softer suspension than the BMW 7 Series and Audi A8. My test car came with the Airmatic suspension system, which automatically adjusts the damping characteristics of each wheel according to conditions and the driver's driving style. There's a "sport" setting that firms up the suspension and enhances road contact, according to the owner's manual. However, the difference is much less pronounced than in the BMW ActiveHybrid 7, which has "normal" and "sport-plus" settings, in addition to "comfort" and "sport."

The S400's electronic transmission is operated by a stumpy lever on the steering column. Basically, you put the car in "Drive" or "Reverse" and go. However, there are steering-wheel-mounted paddle shifters for those who want to do the shifting themselves. The transmission goes into manual mode when you use the shifters, and reverts to automatic if you don't use them for a while.

The S400 has the same roomy, elegant, wood-trimmed interior as the regular S-Class sedan. Fit-and-finish is impeccable and the seats are extremely comfortable. However, I find Mercedes' Comand control system complicated and not very intuitive. It isn't obvious how to do something simple like change the radio station or alter the map display in the navigation system. Once you master its intricacies, the system is fairly easy to operate. But it takes a lot of trial and error to figure out.

The S400 is available with all the high-tech options found on the S550—though, as always in a Mercedes, at a price. Major options include a night vision system ($1,740); power-adjustable, heated, and ventilated rear seats ($2,990); and rear-seat entertainment ($2,990). A Driver Assistance Package ($2,900) monitors the road ahead and engages the brakes if danger looms, monitors the driver's blind spot, and sounds an alarm if the vehicle goes over lane markers or the driver seems drowsy.

A $4,950 premium package includes everything from heated and ventilated front seats (with massage function), an electronic trunk closer, and a rearview camera to headlights that dim automatically when they sense oncoming traffic and a parking guidance system that sizes up potential parking spots and provides assistance. A pair of sport packages ($5,800 and $6,550) add "AMG"-style wheels, bodywork, and tires.

Buy It or Bag It?

The pros and cons here are clear. On the plus side, the S400 costs $3,650 less than a conventional S550, will save the average owner about $400 annually in fuel costs based on government estimates (and more if you do a lot of in-town driving), and qualifies for a federal tax credit of up to $1,150. The S400's starting price also is some $14,000 to $21,000 less than comparable BMW and Lexus hybrids. Oh, and the S400 pollutes less than a conventional luxury sedan.

Though pricing hasn't been announced, the S400 will remain almost unchanged in 2011, with dark eucalyptus-wood interior trim and 18-in./10-spoke wheels being the main new options.

The S400's downsides: It isn't nearly as quick as the S550 and its main competitors. Also, it isn't available with all-wheel drive, while the S550 and Lexus LS 600h L are.

So, if raw acceleration and all-wheel drive are priorities, you can drop the S400 from your shopping list. If they aren't, the S400 is well worth considering, even if you aren't necessarily shopping for a hybrid.

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