Wet pumps have no seals, per se, and in fact get their lubricating oil
from the accessory pad they are driven from. On many engines this means
that the seal is removed from the drive pad. Internally, the pumps have
either steel (ARO), or heavy graphite (Pesco, Garwin) vanes that do
eventually wear out, but you would tend to see this wear indicated by
poor vacuum, rather than extra oil. The typical "output" of these pumps
is a lot of air with a fair amount of oil entrained, almost like the
spray from an aerosol can. The engine breather vent should have almost
no oil at all, and at extremely low pressure (inches of water, rather
than PSI). Unfortunately, most air/oil separators don't do a very good
job. I've tried 4 or 5 different units, and only the Airwolf did what it
was advertised to do.

JFLEISC wrote:
In my continuing effort to plug all the oil leaks in my Continental 0-300 I
have a final question about wet vacuum pumps. How much oil out the vent is too
much? This is a '61 C-172 with the factory standard oil recovery system off the
wet vac. About twice as much oil comes out the vacuum vent as out the engine
vent. Is that normal and if not what is the fix? Are there seals in the pump
that wear out or something? Any info would be appreciated.

Jim