Naf --

It has been well documented that substituting automotive oil in an aviation
engin eis a BAD THING.

In fact, it is so well documented that I can't find references to it
anywhere.....(Actually, I'm at work and all my reference stuff is at home)

The guy to talk to is Ben Visser at Shell Oil Company.  He has also given
numerous seminars at Oshkosh on the topic.  I remember reading an article
that he wrote for one of the general aviation publications within the last
couple of years.  Unfortunately I don't remember any of the reasons WHY it's
bad to use Castrol 10W-30 in your Lycoming, I just remember that there were
many reasons.

Try a web search under "Ben Visser", try the Sacramento Sky Ranch book, or
call Shell Oil and try to talk to him directly.  Let us know what you find
out.  Sorry I couldn't be more helpful, but at least it's a start.  But
PLEASE don't use car oil until you do this research.

- Rob Wolf