Herb Sanders wrote:

Hi Paul, I attented a Shell forum at Oshkosh several years ago and the
Shell engineer conducting the program stated that 100% synthetic oil
would not hold lead in suspension, but would allow it to precipitate out
and coat internal parts, create sludge, restrict circulation, etc. Lead
and synthetic is a problem. The Shell 15/50 is about 50% mineral oil and
will hold the lead in suspension to be drained out.  This may not be a
problem in the 13B since the crankcase oil is closed to the combustion
process.

No one asked a question about synthetic 2 cycle oil. Do you know if
mineral 2 cyc oil would absorb lead while in solution with gas? Does lead
in avgas accumulate in the seal groves? Maybe someone would know if best
to use mineral two cycle oil/ or synthetic 2 cyl oil over the long term
with leaded gas. It is not going to be easy to find unleaded gas on XC
flying.

Regards, Herb Sanders

According to Tracy's idea it is closed better than I thought
it was. At least for a normally aspirated engine with
side oil seals in good shape.

Tracy has the most experience in these matters and even 
Marvel Mystery Oil is working for him so maybe we are over
blowing this problem. Perhaps I need to test MMO at 400 F.
He is running the engine harder lately so the apex seals
are probably running hotter.

Obviously Tracy is changing his system oil every 50 hours or
every  six months for the average aircraft use so the system oil
does not appear to be a big problem. Tracy does burn 100LL
from time to time. 

Paul
 
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