Last year, BMW introduced a new eight-speed automatic transmission plus a new turbocharged four-cylinder engine in the base 328i Sedan models, which gave BMW 3-Series a big boost in fuel efficiency. Those efficient powertrains continue into 2013, but this year there's also a new ActiveHybrid3 model.
Unfortunately, with a turbo six instead of a four-cylinder engine under the hood, the ActiveHybrid3 likely won't much more fuel-efficient than the 328i and 335i models--both earning up to 23 mpg city and 33 or 34 mpg highway. But with a supplemental electric-motor system and 675Wh of lithium-ion cells in the trunk, it boasts an all-electric range of 2.5 miles--a feature that could boast real-world mileage in stop-and-go driving significantly, if you can show some restraint. The system can also shut off the gasoline engine when coasting at high speeds (up to 100 mph).
All 2013 3-Series sedans also 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.
Going turbocharged has a very positive effect on fuel economy. BMW 328i models with the automatic earn 34 mpg on the highway, which is on par with some four-cylinder mid-size sedans that aren't nearly as exciting to drive.