With turbo four- and six-cylinder engines, smart eight-speed automatic transmissions, as well as fuel-efficient clean-diesel and hybrid variants, the 2015 BMW 3-Series offers surprisingly many options for those looking to be frugal and green. You might be mistaken for being less environmentally responsible, but there could be some fun in that.
First, let's get the disappointment out of the way. Unfortunately, with a turbo six instead of a four-cylinder engine under the hood, the ActiveHybrid3 likely won't be 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 has an all-electric range of 2.5 miles--which could significantly boost real-world mileage in stop-and-go driving. One thing that's quite noteworthy about the system is it can shut off the gasoline engine at up to 100 mph, when coasting.
As for the 328d, it's more efficient in real-world driving than the ratings suggest -- and some have seen above the EPA's 45-mpg highway rating.
Real-world mileage is very impressive in the 3-Series across all the gasoline models, and you'll likely manage to meet the EPA ratings with a rather light right foot. 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.
Separately, the air conditioning compressor is now 'smart' and the coolant pump only runs 'on demand.' And if you select the so-called ECO PRO mode, you get a softer throttle, earlier shifting, and leaner accessory operation, all aimed at maximizing mileage.
It's also worth noting that the entire 3-Series lineup, whether you go for the Gran Turismo or the base 320i sedan, gets 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). Brake Energy Regeneration system is also included in some of the model line; it saves the most aggressive operation of the alternator for when you brake, which pays off with better fuel efficiency the rest of the time.