Here's the final answer. Buried deep in the owner's manual, in fine print, it says not to use BIA or TCW (2-stroke water-cooling type) mixed oil. The oil I use for the outboard is TCW oil. Whatever the heck that means. So off to Simpson Hardware I go for the correct oil. As for the gasoline, we are blessed with at least two stations in Sumter, SC that sell ethanol-free gas. Plus, there's a Shell station on the way to the sailing club that sells it. Ethanol will never cross my small engines' lips!
as for the mixing oils for a two stroke engine.... it absolutely DOES make a difference whether its an air cooled motor or a water cooled motor..
for
air cooled engines, and this includes some of the lower end outboards, you must use an oil
recommended for use in air cooled engines, such as a mixing oil for chainsaws.
ace hardware sells the "master mechanic" brand, which is specific for air cooled engines.
in a
water cooled engine, you can actually use either the air cooled formulation or the water cooled formulation as there are no "hot spots" in the water cooled engine like there are in an air cooled one.... no damage will will result so you are good to go with either oil.
(even though its safe to use either oil, I do like to see the instructions stating to use an oil formulated for water cooled engines, as this shows that the manufacture of the equipment recognizes there is a difference in the two formulations)
the TC-w3 rating is a recommendation that
all of the manufactures of water cooled 2-stroke oils have adopted, and
some of the manufactures of air cooled 2-stroke oils.
in the literature explaining the TC-w3 rating, you never see anything said about air cooled engines, chain saws or leaf blowers.... but you will see mention of water cooled 2-stroke engines.
in a nutshell, the actual difference of the TC-w3 forulation of the oils is about the same as the difference in ON-road diesel and OFF-road diesel.... one is supposedly better for the environment than the other, but does nothing to make the engine run better....
you may be able to get by with the wrong oil for awhile, but the wrong oil in a
hard working air cooled engine will cause scoring of the cylinder walls and loss of compression (power, and the ability to start up)... and then you throw it away and get a new one....