The engine block needs to be vented to the air from a point as high above the oil level in the pan as is possible. The cap seals tightly but the filler tube has a small pipe sticking out the side to provide that vent. The stock little tube works fine in a street engine and all or part of this breather is run back into the intake for pollution (legal) reasons.

 

In racing we use at least a dash 10 hose size for that venting operation. It is the path for gasses escaping past the combustion seals in hard use (like racing or airplanes). Not venting will pressurize the crank case and defeat the front or rear main seals, and make a huge oil leak.

 

On shutdown, local air is pulled into the engine as it cools to ambient. That air will have humidity in it. At night the water condenses out of the air and a few drops of water will run down into the oil supply. As the engine is used again the oil temps get to 160 or more and most of the water is forced out of suspension and you will see a bit of water drip from the crank case breather hose, or find some in the catch tank if you have one. This output may be a sickly white and frightens many into thinking something is wrong, but this is normal for all engines and not peculiar to a rotary.

 

Lynn E. Hanover