All 2012 3-Series sedans get Auto Start-Stop, which shuts off the engine at stoplights, as long as automatic versions are in Drive or manual versions are in a gear (with the clutch and brake depressed). All models also get the Brake Energy Regeneration system that BMW has already installed in some of its other models; it saves the most aggressive operation of the alternator for when you brake, to help aid fuel efficiency the rest of the time. The air conditioning also includes a new ‘smart’ compressor; the coolant pump operated ‘on demand,’ and there’s an ECO PRO mode that includes driving-style coaching and operates ancillaries in their leanest modes.
The Auto Start-Stop system can be pretty rough with the six-cylinder—delivering more of a shudder/kick than we’ve felt from other systems—but it’s smoother with the four.
There’s no disputing that the net effect is great gas mileage. BMW 328i models with the automatic earn an almost incredible 24 mpg city, 36 highway (manual models are 1-2 mpg lower), while the 335i with automatic gets an excellent 23/33—those are figures on par with some four-cylinder mid-size sedans.
At the time of posting, there’s still no official word on whether the new BMW 3-Series will return in 335d diesel form (or whether a new four-cylinder diesel will be picked instead), but the automaker has said that there will be no U.S. 3-Series diesel until at least the 2013 model year.