Another point that has not been mentioned. Most marine oils and in
particular TWC3, are designed to protect the engine at mixtures of
50:1 in premix, or in injection systems where the mixture can approach
100:1 under light loads and 50:1 or more under high loads. This is to
reduce polution in both air and water, as well as reducing engine
buildups in high output engines.(some even run 100:1 in premix)
In comparison, my chainsaw specifies 16:1 (it's an old saw) and many
other small 2 strokes specify 25:1 or heavier mixes. You most
certainly can NOT use the standard oils designed for 16:1 or 25:1 at
40:1 or 50:1 and expect proper protection.(for instance in watercraft
or snowmobiles) You also cannot expect the chain saw to be properly
protected by a 50:1 mix of TWC3 oil - and a 16:1 ratio of TWC3 for the
old chainsaw does not make any sense either. Would likely give
adequate protection, but the TWC3 does not burn as well (oxidation
inhibited) so the oil basically flows right out the exhaust either as
unburned oil or very copious amounts of thick smoke.
The best idea is to use the recommended oil for the
engine/application.