based on ur saying... the electrical fan only works when the sensor tells it to do so if the engine is too hot and it needs fan to support it. But my e36 323is 1998 does have two fans, one is ele fan and another one is behind the engine and radiator.
As u said, thermostat, water pump and radiator are brand new, with new silicon radiator hoses. It seems like u need to check the hand gasket.
also the bleed screw, make sure there is no air lock in ur cooling system.