Mercedes-Benz will not entertain three cylinder engines in its larger rear-drive saloons, but the configuration could appear in smaller models
10 March 2014

Mercedes-Benz has ruled out three-cylinder petrol and diesel engines for its main range of rear-drive saloons, despite rivals like BMW adopting the fuel-saving technology.

"We have looked at three-cylinder engines, but there are too many compromises, such as refinement and the savings aren’t that significant," Bernhard Heil, head of engine development said at the Geneva motor show.

Heil says Mercedes has experimented with three-cylinder engines, but the vibration and loss of refinement, particularly at low speed operation when fuel savings could be maximised, are too big a penalty to pay.

Mercedes is gearing its engines to operate at as low a speed as practical, a strategy Heil calls ‘Down-Speeding’.

To boost refinement, three-cylinder engines need balancer shafts, which add weight and cost and wipe out many of the advantages of the smaller swept volume.

Mercedes is, however, likely to develop a second family of slightly smaller-capacity diesels with a swept volume less than today’s ubiquitous 2.1-litre OM651 unit.

The OM651 is increasingly popular, powering around 70 per cent of all rear-drive Mercedes models. Heil didn’t specify a capacity, but 1.9 or 2.0-litre capacities are possible alternatives.

The powertrain of front-drive models like the new A- and B-classes, could however, be powered with three-cylinder units.

Although these engines would need balancer shafts, Heil says the packaging advanatges would allow Mercedes to add a motor/generator unit between the front wheels for future hybrid applications.

Our Verdict

Mercedes-Benz C-Class 2007-2014
The C-Class rivals the likes of the Audi A4 and BMW 3 Series

The Mercedes C-Class marks a return to the company's old-school values of all-round quality and maturity

Add your comment

Log in or register to post comments

Find an Autocar car review

Driven this week

  • Car review
    21 October 2016
    Can Seat’s first SUV impress, even with the heavy burden of expectation?
  • Car review
    21 October 2016
    The last hurrah for the current Aston Martin Vantage adds the track-ready GT8 to the range
  • Audi S5 Sportback
    First Drive
    20 October 2016
    New S5 Sportback is more spacious, better to drive and offers a calmer ride than before, but rivals offer greater involvement
  • Renault Clio RS 220 Trophy
    First Drive
    19 October 2016
    Mildly revised hot hatch is enjoyable on UK roads but continues to play second fiddle to the Ford Fiesta ST
  • 2016 Smart fortwo Brabus cabrio xclusive
    First Drive
    18 October 2016
    Mechanical upgrades make the Smart Fortwo Brabus cabrio better to drive, but it’s too pricey to recommend