Thermostat going bad is not uncommon.

Also, since you have the system open, replace your coolant expansion tank while you are at it. They go bad anytime after 60k miles. Good time to check your belts, hoses, idler pulleys, etc. while you are messing around in that area.

Good luck!

__________________
Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual