Evinrude said never mix. They found some brands of gear case oil when mixed would combine and foam causing enough pressure to rupture seals. The very first synthetic outboard oil was made by Lenard Refineries in Michigan. A few months after tentative introduction it was found to react in combustion with a winter gas additive used by a Wisconsin refinery to form a super glue. Dad made Lenard a distributer so they wouldn’t go bankrupt over the 1000 plus outboards they replaced under there oil warrantee in south west Michigan. The oil was quickly pulled from the market as was the ad campaign. Lenard pretended it never happened. A lot of off brand outboard owners were very happy with there new Evinrudes . . . 😆
