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Re: Audi Oil Filters

   > You've still got a whole block full of oil galleries that can drain back
   > through the oil filter . . .

   Ummm.... what? (insert dumb look here) :) I dont understand that 
   statement... the galleries are not in the oil filter itself, so they 
   would not drain out the filter. If they drain through the filter  as you 
   say, that would only FILL the filter back up with oil!
   I think Im losing it! :)

I'm sure you lost it a long time ago (I know I did) . . .

Consider the low-point in the oil system (gravitationally-speaking) is
the pan. Above that is the oil pump, which then pumps through the oil
filter to fill the engine "above" the filter with oil. All that oil in
the engine oil galleries, when not under active pressure driven by the
oil pump, wants desperately to maximize entropy by falling back down
into the pan. If the oil filter has a one-way valve, then the oil is
effectively trapped in the galleries, and immediately available to
finish being pumped by the oil pump through the bearings and back to
the pan normally. Any oil that manages to drain back into the pan via
the filter and pump leaves a "vacuum" (lack of oil) in the engine
which has to be refilled by the oil pump the next time you start your
engine -- leaving "several" seconds of the engine left running on
whatever oil residue is left over from the last time you ran the
engine, rather than a nice high-pressure oil film to float all the
[plain, as in crank/etc.] bearings. It is even conceivable that, in the
worst possible case, that the oil pump could completely "dry out" and
not be able to prime itself . . . (I once had to "prime" an oil pump
by pumping oil backwards through the oil pressure gauge feed line...
'twas a completely new clean dry oil pump...)