BMW Repair: Engine cooling system problem, engine cooling system, expansion tank

Question
OK heres the situation: 2001 325i sedan. I noticed from the original purchase date (purchased it used in 03),the need to add coolant every few months, which means it likely had a slightly leak.About 6wks ago my coolant light would periodically come on while driving.When the light came on,sometimes itd remain lit for the duration of the drive sometimes,other times it would only stay lit for a minute or 2 then go off.The light came on randomly even if I just topped off & car ran great so I ignored most of the time.This started about a month ago.Then about 3weeks agoI noticed a slight smell coming from the car so I ran the error codes.It indicated the map controlled thermostat. The part was replaced with a new one,but immediately after installing it the vechile was started without bleeding it 1st.Apparently, this caused the expansion tank to become overpressurized &crack.So we purchased the part and installed.This time we remebered to bleed it however when attempting to turn on the heat blower again noticed the air was far from hot even when set to 91 and blower manually on high.I live in a hot region so i likely used my heater 5 times/yr so I dont know how long this problem has been active.Yet the previous error code were now gone & no new codes had appeared.When researching the issue it seemed the common cause of this was most likely cause of lack of heat being transferred was tjhe result of a heater valve malfunction.So again part replaced.No error codes.Still no heat,but we continued to attempt to bleed the air out but with the car in pos 2 and the "suppose to be heat" blower on no bubbles came out.Nothing came out.I know the system has air trapped in it because if I start the car without the bleed screw open the expansion tank is forced upwards from the pressure trapped.We reinstalled check the clamps on the bottom of expansion tank,all hoses and correlating clamping and everything was tight.This time we tried starting with the bleed screw open it shoots out steam on start up but then stops slowly while sitting idle for a min.How can I bleed without heat? In attempting to correct the no heat issue the heater valve was replaced.No hanges in status.If we start with the bleed screw open it starts up ok shoots out air then slowly stops.Still the no heat from any of the interior vents.No error codes. What direction should we go with this? Pls advise.  

Answer
Brock, once you have most of the bubbles out from the bleeder screw. Close it make sure the resevoir is full and run the motor with the heater on high heat and minimal fan speed. Drive the car. You need to heat cycle the motor from cold to hot a couple of times. Top off the fluid with motor at room temp. Make sure you are getting the motor hot. Run the motor at 3000-3500 until the mechanical fan clutch engages and delivers enough air that you can feel all the way back at the windshield. Make sure the center vent thumb wheel is set to hot (red). Let me know if this works or doesn't. BMW's use coolant. I don't know why but they will need topping off every couple of months. Make sure your radiator cap pressure tests okay also.
-Evan