My recollection is that the key difference with aviation oils is the
additive package.  Auto oils are 15%+ additives, and because autos burn
virtually no oil, the additives are formulated accordingly using the
chemistry the manufacturer's judge to be best.  In contrast, aviation
engines burn lots of oil under much different conditions (high
temperatures, continuous high power).  Consequently the additive
packages are very different.  More importantly, the additives in
aircraft oil are "ashless" meaning they will not burn and leave deposits
in the combustion chamber that can cause mis-firing and detonation.  So
the word on automotive oils is, they are fine for automobiles, but could
cause major detonation problems in your Lycoming or Continental because
of the oil consumption in the big air cooled engines.

Fred Moreno