Is Marvel Mystery Oil® safe to use in today’s “high-tech” cars?
Yes! Marvel Mystery Oil is completely safe in today’s high-tech cars and provide the same benefits as it has since 1923-cleaner engines, upper cylinder lubrication, reduced acid and sludge build up, improved fuel economy, clean and lubricated fuel systems and many more!
http://www.marvelmysteryoil.com/index.php/site/faq/
I run 2 gallons of avgas with 10 gallons of unleaded for the lead. It also makes the exhaust gas smell better.
I use MMO in a pinch.