BMW Repair: Overheat, expansion tank, 1999 bmw 323i

Question
My last 7 digit VIN is CD55033. My car is 1999 BMW 323i (E46). The car had overheated before and I had replaced water pump, expansion tank and expansion tank cap. It worked for a while without overheating even though the "add coolant" light came on once in a while. I added coolant every time the light comes on. The other day my brother drove and the car overheats again. He forgot to bleed after adding the coolant. He turns off the engine as soon as the temperature crossed over midpoint. It never reaches the red zone. I checked your website and follows the instruction how to bleed the cooling system. The first time after I bleed the system, I drove 1.9 mile before it starts overheating again. I turned on the heater while test driving. Only cold air come out with air con off. I check the hoses on either side of thermostat. The left side hose coming out of radiator is cold but the right side hose connecting to expansion tank is hot. The temperature reaches midpoint in 1.1 mile. I let it cool down and release the bleed valve and air come out. I tried to drive about 1.7 mile and bleed it twice more. On the last time with the heater on, the heat starts to come out of the vent and it seems to be fine. But the fan was not on. I let the car idle for 15 minutes while turning the heater off to see the fan will come on. But the fan would not come on. The temperature hold on at mid point. The fan was on last couple of days and I was wondering whether it has to do with turning the heater on inside. I have not tried further by driving more than 1.7 mile since I am kind of afraid, it would overheat again. I would like to ask your expert opinion before I tried to drive a little more further. Do you think it is the thermostat or the fan? I check the spark plug and dipstick and both does not have coolant in them. It does not have any white residue and the exhaust does not spew out white smoke. BTW, I replaced the expansion tank cap again and the "add coolant" light is not on anymore when the overheat happened. I was hoping I could DIY @home without costly repair bill. Your expert opinion is greatly appreciated. Thank you.

Regards
Ryan

Answer
Ryan, I would replace the thermostat due to the fact that you said overheating was taking place and the lower radiator hose was not hot. This means that the thermostat is not letting the cooled coolant back into the head and block as you said that the car was showing over temp. on the gauge. The radiator could be clogged internally, but by experience I haven't seen it on BMW's. Replace the Map thermostat assembly. Also recommend an upper radiator hose due to the O-rings in the hose have difficulty resealing after being over heated and removed (if not replaced recently). Use a 50/50 mix of anitfreeze and water. BMW coolant preferably (I know it is pricey). Pressure test the cooling system and bleed of air. Start up the car and turn the heater on low speed, full hot. Get a good floor mounted fan you can put in front of the radiator if the car overheats. After idling a while turn the climate control to full cold and make sure the snowflake button is pressed. Check auxiliary fan operation. If your A/C system is full on charge and the motor is at operating temp at idle the fan should turn on within a minute. If it doesn't replace it. A faulty Auxiliary fan will work intermittently so keep an eye on it. If fan operation is good and temp is stable then it is time to get it hot and test the mechanical fan clutch. With the clutch disengaged at idle you should be able to carefully slow and stop the fan with your hand. With a second person in the driver seat give the motor 2500-3000 RPM and keep it there. Let idle if overtemp occurs of course and turn on your floor fan. You will need to give it maybe 15 minutes of this higher RPM to get the Mechanical Fan clutch to engage. When it engages it will sound like an airplane taking off. Unmistakable you will feel hot air all the way back at the base of the windshield. If this engages then test drive. And you should be in the clear. Let me know how it goes.
-Evan