Have been told that 4-stroke outboards from all makes; Yam-Hon-Suz-Merc are designed for traditional oil, and not synthetic. Talking about the 5-qts or so for the outboard's crankcase. I use the 5qt/$15 Wal-Mart price in the big yellow bottles from Valvoline, (20w-40 or something?) because I like the name Valvoline and the color yellow, and then recycle the old oil and old oil filter at the Meredith transfer station!
Both Shep Brown's and Y-Landing sell the factory oil filters which are only about two dollars more than a similar Fram oil filter at Wal-Mart so I spend the big money on a factory filter. Plus, Wal-Mart's Fram filters are designed for cars, and not outboards, if that even makes any difference?
Plus, I go through Mystery Oil like it was cheap red wine, and have been told that using Mystery Oil in the gasoline mix is a NO-GO for engines using synthetic oil, because the two do not mix together. Sort of like water and oil; synthetic oil and Mystery Oil.
Anyone put any Mystery Oil in with the crankcase oil, and not just into the gasoline? Mystery Oil is some type of a detergent and makes the engine insides clean of the evil sludge!