Yamaha would like for you to use "their" oil. But any Major brand (key word MAJOR) oil that is TC-III will work. However you do NOT want to mix brand A and Brand B together in your reservior. Some oils do not mix well with each other and can turn into jelly. Whatever you do. NEVER buy oil in some convienance store where the oil is setting on a sun drenched shelf. That is unless you want to buy pistons. But like said, any major brand oil, Mercury, Johnson, Evinrude, Suzuki, etc etc. Also a word of caution.....READ THE LABLE. A lot of the marine oils are sold next to each other on the shelf. One will read " 2 stroke" one will read "4 stroke" and some will simply say, "For Marine Use" That catch fraise, For Marine Use, could mean for either 2 stroke or 4 stroke. Buyer Beware.
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mike halfmann