2000 BMW 3 Series heaters r working, but blowing cold, and overheating??

Is your antifreeze at the correct mixture /, if not you have frozen the coolant resulting in the water pump impeller shearing off.
If it has not frozen then check/change the thermostat first, post back the result please.

Get a sniff test ( block test ) carried out to check head gasket .

hi thankyou, we have changed the waterpump and the thermostat and thermostat housing, and all seemed good, nice hot heaters then after 4 miles all went cold and a few more miles down the road the water light came on and lots of air came from the bleeding screw.. any suggestions??

hi thankyou, we have changed the waterpump and the thermostat and thermostat housing, and all seemed good, nice hot heaters then after 4 miles all went cold and a few more miles down the road the water light came on and lots of air came from the bleeding screw.. any suggestions??

Is the car losing coolant? if so make sure it`s not just leaking out somewhere.
If it isnt you should get a sniff test done as suggested by Whittinghame.

Classic symptoms of head gasket knackered .

Sounds to me like you have an air lock, or a blockage may be in the rad, try drainig all of the water & antifreez into a bowl so you can re use, then try flushing the system with a garden hosepipe until water runs clear, if not sure on what to do, look in the haines manual hope this helps.

hi there my 3 series been doing the same had to change f.s.u for the blowers to get hot again but the overheating problem was the secondry water pump when i remove it and join the two pipes together i have no probs but when i put a new one on it starts overheating, try it but im still trying to find out why it overheats with this pump on the car