Mercedes-Benz S 400 BlueHybrid first drive

What is it?

This is the Mercedes S 400 BlueHybrid, the company's first production hybrid. Mercedes has developed the drivetrain technology in a joint venture with BMW, which plans to use it to underpin the similarly conceived 7-Series ActiveHybrid.

Visually, little distinguishes the Mercedes S 400 BlueHYBRID from the car it's based on, the three-year old S 350.

There are no aerodynamic tweaks or changes in ride height, only subtle BlueHybrid badges serve to give the game away.

What's it like?

The S 400 uses a lightly reworked version of Merc's existing 3.5-litre V6 petrol engine, with a new cylinder head, lightweight pistons and a reprofiled crank, although it does without the direct injection that Merc uses in other applications.

Output increases by just 7bhp over the S 350 at 279bhp, with torque remaining the same at 258lb ft.

The clever bit is the disc-shaped three-phase AC electric motor mounted within the front of the gearbox housing, and providing additional thrust when required, output swelling to 299bhp and 284lb ft, with drive channelled to the rear wheels via the standard seven-speed automatic gearbox.

The new system does not support pure electric propulsion like that offered by the Lexus LS600h; the efforts of the electric motor are used exclusively to boost those of the petrol engine.

This is also the first mass-produced hybrid to use next-generation lithium ion battery technology. It weighs just 27kg and provides more efficient charge and discharge than the nickel-metal hydride batteries used by other hybrids.

It's also compact enough to fit in the position normally used by the S-class's standard battery at the base of the windscreen, where it's cooled by a patented process linked to the car's aircon system.

The S400 BlueHybrid doesn't demand any particular change in driving style. In fact, it feels a good deal like the S350, only a touch more powerful under acceleration in lower gears.

On the open road in taller gears, the added output is not immediately evident, owing in part to the added 75kg brought on by the hybrid system.

Mercedes-Benz claims 0-62mph in 7.2sec - just 0.1sec inside the time it quotes for the S350. But the emphasis here is not on out-and-out performance.

Rather, the S 400 BlueHybrid has been conceived to provide optimal fuel economy. And on this front, it is rather impressive.

A claimed combined average of 35.8mpg betters that of the S 350 by 8.4mpg, relating to an overall gain of 165miles in range on its 90-litre tank.

Equally impressive is its CO2 rating, which at 190g/km betters that of its pure-petrol sibling by 57g/km.

Should I buy one?

Pricing details have yet to be confirmed, so that's a difficult question to answer. But, on first impressions, this is a thoroughly well-engineered car that moves the hybrid game along by some margin.

Unfortunately Mercedes has no plans to build the S 400 BlueHybrid in right-hand drive, meaning UK sales will be special order only.