Have you been watching the coolant level? Have you had to add any?
Possible that the car had some cooling system work before you bought it, and it wasn't bled properly (the six is very difficult to bleed, and s/b done by a BMW specialist).
The lack of heat is a tip-off that there is air in the system. If you are losing coolant, there is a leak, which allows air in.
Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.