OVERHEATING!!!!!!! my car began overheating on a 6miles in to a 8 mile drive, it had a small crack in the rad' which i changed the next day, i bled the rad' ran the car again and it overheated. So far i have changed the water pump, thermostat, all water pipes, taken the head off, had that skimmed and pressure tested, new head gasket and blocked off the heater matrix to eliminate that from the coolin system and still it continues to overheat, it looks to have poor circulation as pressure builds up in the rad, pipes and hoses after 5-10mins of running and can be seen rising in the expansion tank!! is there anythin else u can think of that i may of missed????

Ilragatzzo78 is 100% right.  I had the same trouble with my 318ti.  It took a lot of sitting on the side of the road.  The only solution is time.  Bleed, bleed and re bleed.  You can bleed it through the bleeder screw on top of the radiator (plastic screw).  I didn't know about the angle part, but thanks for the idea..
Nick

Nooooo.
that's the problem
yes, you have to take the coolant filling cap off " expansion tank cap "
turn your car on for at least an hour
the bmw line has a very bad problem wich is " bubbles " inside your water system
you have to have your car inclined and running without the cap so he can bleed all the bubbles out.
sorry you spent all that money but after you replaced the radiator all you had to do was that, to get rid of bubbles.

so, do this. park your car on an incline position, engine up.
remove the cap. let it run for at least an hour.
refill as needed " coolant "
do that the following morning and for last refill the collant as needed.
problem should desapear.
hope this helps