The crankcase breathers I've seen allow air out of the crankcase
when the piston goes "down", or into the crankcase. When the
piston goes up, the valve closes. This maintains a very slight
negative pressure, and helps cut down on oil leakage.

--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
..

"Meat Plow" wrote in message
...
:
: Crankcase breather traditionally allowed some outside air
through a filter
: membrane of various shapes and designs located somewhere on the
engine to
: mix with the crankcase air during operation. But come to think
of it with
: today's tight emissions, crank byproducts would get
recirculated back
: into the engine via a shunt into the intake manifold. If this
is the case
: then you could be seeing this in your filter because of an
incomplete
: sealing of a valve causing excessive blow back pressure in the
manifold.
:
: