I just had this last week. My indy had fitted an Autozone thermostat last year because I had not supplied one when I dropped off the car and, with Christmas coming up in a few days, neither of us wanted to wait for the replacement to be shipped.
Fast forward 11 months and there we went again. A FCP supplied thermostat later and the needle (and temperatures according to my always plugged in Scangauge) are back to normal range.

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2015 X5 xDrive35i MSport
2013 X5 xDrive35i