Hard to believe.... No way. X6 3.5i is rated 15/20 - see specs on the bmwusa.com. You cant possibly get combined 21.19 with these city/hwy ranges.

Something is wrong with the numbers they posted for X5 3.5i...

BTW, my 335i with N54 is rated at 17/26, and I am averaging 20mpg. And that is for the much much lighter vehicle.

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His : 2013 X5 3.5d Deep Sea Blue/Black/Aluminum with ALL packages, 20" 214"s, running boards, Adaptive Drive, Spare Tire, BMW Apps
On Order : 2016 X3 3.5 MSport Silver/Mocha with DHP, CW, Prem, Tech, DA, Lighting

Hers : 2015 328xi MSport Silver/Red

Prior:
2008 X5 4.8
2011 X5 3.5d
2010 335 xDrive
2013 335 xDrive