That little thing can wreak havoc on an engine. In my case I believe the engine was not breathing and building up pressure in the motor, thus forcing oil through the seals which were leaking on the manifolds causing the smoking.
When the tech was looking at my boat, he removed the oil filler cap and the boiling noise went away immediately. That got my wheels turning that it was an internal pressure issues. Some googling led me to the PCV valve.
A bad PCV valve or related component can produce a number of symptoms. For example, if the valve gets stuck in the closed position or clogs, you’ll notice one or more of these symptoms:
Increase in internal engine pressure
Failure of one or more oil seals or gaskets
Engine oil leaks
Moisture and sludge buildup inside the engine
Engine surges and possibly black smoke
http://dannysengineportal.com/pcv-va...bad-pcv-valve/