Two problems related to crankcase (pcv) have been reported for the 2004 BMW X3. The most recently reported issues are listed below.
While driving at freezing temperature, white smoke came from the engine room. I stopped the engine and found huge leak of oil from the valve cover. I needed to add 1 quart oil which mean 1 quart of oil was leaked out. I had a mechanic look at it and was told that the leak was caused by freezing oil separator. Since the oil separator was designed incorrectly, it stops working by the frozen condensate in cold climate. And, it cause high pressure in the crankcase and consequently oil leak through the valve cover gasket. The problem may cause a complete engine failure.
Failure of crankcase ventilation valve in 2004 3 series BMW. This failure was caused by moisture build up in the valve, which then froze at an extremely cold temperature, causing the engine to seize. Apparently, BMW has known about this problem, as the replacement valve is "re-engineered". Apparently, this problem only occurs in the six cylinder engine, at extremely low temperature, and in cars which are used only in "short trips". The car has been down for over two weeks, awaiting parts.