Re: Synthetic or not…Oil question of the week Home › Forum › Ask A Member › Synthetic or not…Oil question of the week › Re: Synthetic or not…Oil question of the week rook49Replies: 17Topics: 3 July 24, 2018 at 11:20 pm #80048 I use synthetic in every motor I own. I use Sierra’s full synthetic TC-W3 in my outboards. The one thing I don’t use is gas with ethanol in it. Works for me.