looks like yer cooling system was not bled properly or theres an air trap. who installed all the new parts?
tip (if yer willing to ge Dirty!)- find the highest point of yer cooling system that is bleedable, sometimes theres a screw over the therostat and open it. turn on yer heater full blast and leave it that way. fill up the coolant resivour but not completely to the top.
fill up till coolant comes out from the highest point opened. close it and turn on the car and only idle it(don't rev it), squeeze some of the main hoses abit too push out air. monitor the temp and if it over heats again send it to a shop that knows beemers cause it could be internal!!
i'm sorry that i cannot explain it better cause i have to be there!