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RE: Pep Boyz

> Im trying to figure out why everyone wants these higher weight oils for 
> their cars.  If Audi recommends a 10w30, they mean it.  There are a 
> million things to consider with picking the weight of the oil.  If you go 
> to thin, then there is too much metal to metal contact as the shear 
> stress is too high and the film can be penetrated, onthe other hand, if 
> the oil is too thick, it wont reach certain areas quick enough, if at 
> all, and it causes alot more internal friction and power loss as well.
> IMO, use the recommended weight, the manufacture is best able to 
> determine the tolerances of everything in the engine and pick a weight 
> that will work best for everything....
... they may indeed mean it, but their recommendation may be based on
requirements which you may not care about as much as other requirements ...

Most manufacturers today recommend a lightweight oil to ensure that they get
the minimum losses due to the oil viscosity and the highest EPA ratings to
ensure they meet the CAFE.  Using a lighter weight oil is more likely to
cause increased wear in the engine, so it may mean that the service life of
the engine would be compromised in the interest of fuel economy.  If I were
making the choice I would be more likely to vote for not having to replace
the engine ... and be oblivious to the $$$$ I've tossed in the $h!tter by my
lower fuel economy ...

Another thing to consider is that for all but perhaps the newest cars that
recommendation was made based upon the use of "dino" oil and not with
consideration to the wide viscosity range synthetics that are now on the
market.  If your car is spec'ed to use 10W-40 does this mean that the
appropriate synthetic is a 5W-40 or a 10W-50 (for example)?  

For the older cars Audi used to provide a table that showed the recommended
viscosity based on ambient temperature and talked about adjustments based on
typical driving conditions.  On my '78 Fox the engine ran for quite a while
on Castrol 20W-50 exclusively.  One Bay Area winter I decided that I might
want to try running the 10W-40 ... and during that interval the engine which
use little to no oil between changings began to use about a quart per 1000
miles ... which did not go down after I switched back to 20W-50 ... they may
have been unrelated events, but I don't experiment any more ...

Steve Buchholz
San Jose, CA (USA)