Did you change the coolant yourself? If yes did you bleed the cooling system properly? Check the coolant level when engine is cold to see if it is too low and top it off if needed. Get the engine to temp and bleed the circuit using the bleeding screw on the expansion tank. If the bleeding was not done properly air may have been trapped when the coolant was changed which would affect the circulation of coolant through the cooling system. As a result the engine would run hotter than it should. Saw that often on BMWs including mine.