"Dave Stadt" wrote in message
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"mikem" wrote in message
ups.com...
Crankcase fumes are sucked into the induction manifold (and burned by
passing through the engine) via the Postive CrankCase Ventilation check
valve.

The question still remains....how does the moisture escape as modern
engines are not vented to the atmosphere but are a closed loop. We aren't
talking about crankcase fumes but about moisture supposedly being boiled
off into the atmosphere.

'Modern' engines (with PCV for POSITIVE Crankcase Ventilation) are NOT a
closed loop. The atmosphere from the crankcase is sucked into the intake
manifold by engine vacuum (then burned in the engine), the atmosphere sucked
out of the crankcase is replaced by filtered air (either from a breather or
engine intake air filter) and blowby gases. Usually an attempt is made to
induce some cross flow such as by sucking air out of one end (or side) of an
engine and replacing it in the other. This ventilation is maximum at closed
throttle (low manifold pressure) and minimum at full throttle (high manifold
pressure).

AFAIK most aircraft use the older type of crankcase ventilation system
utilizing (what in an automobile was called a road draft tube) a tube cut at
an angle and extended into the airstream to create a lowered pressure. This
system only functions when the tube is in moving air, and on the ground this
is only supplied by the prop wash and is significantly less than the flow
occurring when actually flying. This is also part of the reason that
actually flying is far superior to ground running for removing moisture from
the crankcase.

Happy landings,