Jimm 8/12/2012The overheating condition may be related to; leaking coolant, coolant mixture is incorrect (not at recommended 50/50 water and anti-freeze), faulty thermostat, faulty / clogged radiator hoses, clogged / restricted radiator, faulty water pump, clogged / restricted cooling passages in the engine, radiator fans faulty, faulty radiator fan clutch (if equipped), fan belt stretched or slipping.
Have an inexpensive cooling system pressure test performed - or you can borrow the cooling system tester from any local auto parts store; Advance Auto, Auto Zone, NAPA - for a small fee. Just be sure not to exceed the pressure rating (PSI) on the radiator cap. The cooling system pressure test will help to determine where any leaks and blockages are - for the proper repair.
Bob R. 8/13/2012I assume you have opened the radiator cap and verified that the coolant is circulating once the engine gets warm. If it is not, then the plastic impeller on your water pump has disintegrated as they almost always do by 100,000 miles.
It is essential to bleed the cooling system any time you open it up, or else air in it will impede the normal flow. The bleeder is a small plastic screw plug located near the top of the plastic coolant resevoir (not the radiator). Warm the car up, slightly open the screw to let any air out, and do it again every couple munutes until you only get liquid coolant to come out. Also, you should never run a BMW without a thermostat, and you should only use BMW coolant which costs about $20/gallon at a dealer. Prestone, Zerex, Peak, etc do not agree well with the metals in the engine and cooling system. Change your coolant and brake fluid every two years!