Mercedes sedan ups fuel mileage

Most people don't buy big, heavy, luxury sedans for their gasoline mileage. There are many other vehicles — lower-priced, too — that excel at fuel economy.But government goals for atmospheric carbon reduction, plus competition among automakers, can do funny things to the car marketplace and help...

Most people don't buy big, heavy, luxury sedans for their gasoline mileage. There are many other vehicles — lower-priced, too — that excel at fuel economy.

But government goals for atmospheric carbon reduction, plus competition among automakers, can do funny things to the car marketplace and help explain why Germany's Mercedes-Benz now sells a gasoline-powered, hybrid version of its flagship S-Class sedan.

The new-for-2010 S400 Hybrid is the first mass-production car to use a lithium ion battery to store and supply electric power. The 120-volt battery is more compact and adds less weight to the car than do nickel metal hydride batteries and has high energy density for its size.

The Mercedes S-Class hybrid also has the lowest starting retail price of any S-Class: $88,825, including manufacturer's suggested retail price and destination charge. This compares with the $92,475 starting retail price for a base, 2010 Mercedes S-Class with no hybrid system.

Competitors include the 2010 Lexus LS600h, which has a starting MSRP, including destination charge, of $109,675, and the 2011 BMW 750i ActiveHybrid, which starts at $103,175.

None of these hybrid luxury sedans is a high-volume seller. But each helps address growing government concerns, particularly in Europe, about global warming. These luxury hybrids also can help assuage the consciences of wealthy car buyers who want a big, impressive sedan wearing a badge from a luxury carmaker, not from Honda.

On the outside, the more than 17-foot-long, four-door S400 Hybrid looks like other S-Class models, with traditional Mercedes styling.

Inside, though, the different information displays let drivers know this is a different kind of Mercedes. Even the quiet interior of the car — created by extensive sound deadening plus the gasoline engine turning off by itself when the hybrid system determines the car is stopped in traffic and could take the opportunity to save fuel — adds a new sense of isolation and security for the well-heeled.

The cocoon-like atmosphere continues with the heavy feel to the doors when they are opened and closed and the mass of the more than 2-ton car that's carefully managed over bumps and through twisty road curves and corners.

The S400 Hybrid is the only S-Class offered with a V-6. The others have higher-powered V-8 or V-12 engine. But the 275-horsepower, 3.5-liter, double overhead cam V-6 producing 258 foot-pounds of torque in the S400 Hybrid is supplemented by an electric motor capable of generating 20 horsepower and 118-foot-pounds of torque for added "oomph" while the car is moving.

This Mercedes sedan, however, is a "mild" hybrid, meaning that the car never moves along on electric power alone as "full" hybrid vehicles do.

The get up and go isn't sporty. The car is too heavy for that. But it's smooth and decently forceful. The power system is controlled by a computer that's constantly calculating the optimal mix of gas engine and electric power. The driver just drives the car, and shifts are handled imperceptibly by the seven-speed automatic transmission.

The S400 Hybrid mileage rating is 19 miles per gallon in city driving and 25 mpg on the highway by the U.S. government. I managed nearly 21 mpg during the test drive in a mix of city and highway travel. The U.S. government rating is the best of the S-Class models. The S550, which is the next model up, is rated at only 15/23 mpg. In fact, the S400 Hybrid's fuel rating ties with that of the little, two-seat Mercedes SLK300.

Just as important in Europe, the S400 Hybrid produces 21 percent lower carbon dioxide emissions. Unfortunately, though, the S400 Hybrid uses pricey, premium gasoline.

Mercedes, which has focused on strong, fuel-efficient diesel engines to maximize mileage but doesn't offer a diesel-powered S-Class model in the United States, is late coming into the hybrid car segment. Still, its S400 Hybrid beats the Lexus LS600h in government fuel ratings, though the Lexus has a V-8, instead of a V-6, engine.

But the Mercedes brakes had a spongy, weird feel.

The test car kept passengers well above and away from road surface bumps and jolts. The back seat has exemplary room. I could extend and stretch out my legs, make multiple adjustments on the outboard seats and recline the seatbacks to get comfy. Usually, this treatment is reserved for front-seat riders only.

All around, the interior was elegantly trimmed in leather and wood. I just wished the large knob in the center of the console between the front seats didn't have to obscure the main radio volume control that's closer to the front passenger seat. This knob, by the way, operates the controls and menus seen via the large display atop the dashboard. It has many features but can feel clumsy at times as you scroll through the commands.

And I found I had to turn on the front-seat massage function every time I started up the car. It didn't stay in the seat memory setting.

The lithium ion battery benefit is obvious as soon as the trunk is opened. Unlike the Lexus cars, where the big nickel metal hydride battery pack scarfs up valuable trunk space, the lithium ion battery is in the S400 Hybrid engine compartment. So, trunk space is the same 16.4 cubic feet that's in other S-Class models.

The S400 Hybrid comes with many standard safety features, including some not found in other cars, such as side air bags for rear-seat passengers and Mercedes' Pre-Safe automatic crash protection system.

Intriguing additional features include a radar-connected high-beam headlight system that automatically dims the high beams when it detects an approaching car's lights.

More in Energy