> Actually, I believe the direction of travel is up through the hose
>and into the air cleaner, as opposed to the other way around. The engine
>vaccum sucks the crankcase gasses back through the throttle body. If
>your '94 was anything like my '96, your stock air cleaner would get
>an oily residue on it where the hose attached.
>
>
> -Jon-
Actually, it's the other way. The PCV valve is the vacuum source to the
crank case (from manifold vacuum), the vent hose is the filtered air
input. The oily residue is caused by excessive ring blow-by. Engine
vacuum varies with throttle position and engine load. When the engine is
running and the throttle plate is closed, the manifold vacuum is
high. This sucks out the blow-by in the crankcase. As the throttle plate
opens, vacuum is reduced (varies with engine load, not totally from RPM),
thus less fresh air is being sucked through the crankcase. When under load
for an extended period of time, the blow-by gases will exit through the
vent hose, because there is not a strong enough vacuum signal on the PCV
(under load, the PCV seals itself, preventing oil mist from being sucked
into the combustion process). The oil coming from the vent hose is caused
by oil mist being produced from the crank and rods flying around and by the
engine heat. The mist gets carried out with the flow of blow-by gases.
Anyone that has a manifold vacuum gauge in their truck will understand
vacuum varying from engine load and throttle position. The little filter
mesh that most vent hoses have on them is for trapping the oil mist from
getting sucked into the engine, which causes spark knock.
Mike
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