Crankcase Vent Hose

This tube runs from the oil separator to the lower dipstick tube.

BMW has an ongoing issue with oil separators freezing in cold weather if driving is done before the vehicle is fully warmed up. There is often a howling noise followed by numerous oil leaks. The crankcase breather valve is used to purge the oil vapor from the engine block into the valve cover. However, sometimes condensation can cause it to freeze, causing the entire oil separator system to fail, crack, and disintegrate.

Replace this and all the other components of the oil separator system to prevent damage to all the aspects of your engine. As long as you have everything off, you can rest assured that new parts will last and be reliable.