Oil change & type thoughts ..

[gfl@cc.bellcore.com (grant f lenahan)]

re; Oil type, interval, filter

3,000 miles is a good (balanced) oil change
interval for standard mineral oils.  Synthetics
can go somewhat longer, but you still accumulate
dirt, water, and other nasties.  I change my
Mobil1 at 4,500 miles.

Synthetics are generally better than mineral oils
in a few areas.  First, they resist high heat better -
this is particularly important for turbo cars where a coke
(hard carbon) layer can develop when the very hot turbo
cooks the oil sitting stagnant in the bearing at shut
down.  This is why many companies suggest that you idle you
car 30-60 seconds after a "hard" run (whatever that means).

Second, and third, they flow better when cold and bind
better to surfaces when the engine is not running.  Since
about 90% of wear occurs at startup (no oil circulating)
and when cold (not flowing well), synthetics are better
in minimizing the _real_ causes of wear.

Finally, they break down more slowly.

On the other hand, I know of many people who have
accumulated 200K + miles on Audi's using regular old
Castrol/QS/Valvoline/etc and changing the oil AND FILTER
at 2,500-3,000 miles.

re: filters
All Audis use the MANN 719/5 or equivalent "Rabbit/Golf"
filters.  However, many US and department store brands 
have no anit-backflow valve.  This allows oil to drain
out of the head / hydraulic valves overnight (tapping).
They are _reputed_ (I've no real data) to be less
strong.  This could be a drawback since VW/Audi (at least
the traditional 4cyl and 5cyl engines) do not regulate
oil pressure.  It can become very high under high RPMs
when cold.  Of couse, I used FRAMs (criticized requently)
for about 100 of the 185K miles on my last Audi (sold
with perfect compression), so this may be interesting
but ultimately meaningless.

My answer?  Mann filters ($5/ea from my mechanic) and
Mobil 1, change both every 4,500 miles.  Clean, shiny
cams at ~70k, and I fully expect 250k w/o major work.

Long windedly yours,

Grant
gfl@cc.bellcore.com