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They all have to be SG rated.
The straight single weight oils are superior without question unless you have freezing issues. Viscosity improvers do not clean or lubricate, they just take up space like the plastic peanuts you use in packages.
Then why not use straight 30 weight in your automobiles? People use 10-40 in cars because the 10 weight component gets up into the pistons quicker to lubricate when starting your engine. Any type engine be it on a lawnmower or automobile.