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I recently had a discussion with my automobile mechanic, he has a 17 Montauk with a four stroke Mercury. He told me he has started using 100 octane aviation fuel and his engine has been running better and more reliably.
Question I have. I have an 18' Dauntless with a 135 h.p. Mercury Optimax, meaning I have an oil injected engine. Can I use the 100 octane aviation fuel in this engine.
What year is your engine? Older, pre alcohol gas engines may have fuel line components unhappy with the alcohol content. Newer engines should have alcohol tolerant fuel systems. Some have complained about alcohol gas degrading over time.
Avgas, 100LL, doesn't contain alcohol but does contain some lead and is formulated to be stable/usable for longer periods than auto gas. I, and other boat owning pilots I know, use 100LL in the fall to have it in the tank and engine during the winter.
Cost and availability are drawbacks. I am happy when I find 100LL below $4/gallon and more airports are restricting access unless you have a plane there. If you are buying fuel from the local marina then $4+ avgas may not be a concern but I use the lowest cost auto gas I can find during the season.
If AVGAS is the only alternative to ethanol it may be worth it. Otherwise just buy ethanol free (recreational gasoline) at the pump. You will not get better performance or reliability just because you use higher octane gasoline.
