What’s wrong with 10w30?
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Can’t lubricate as long nor as well as 100% oil.
10W30 is 25% “viscosity improvers.”
10w30 has detergent. SAE 30 is a NON-detergent oil.
Most small consumer-grade 4-strokes use splash oiling, not pressurized oiling systems. Multi-vis oils are really tailored for the latter, to speed oil flow when cold. No point in using a multi-vis oil unless you have a commercial-grade engine with an actual oil pump (and likely, oil filter). Some commercial mower engines are set up that way to help them last longer while mowing inclined or terraced lots.
Also, multi-vis oils thin out faster in air-cooled engines. So 10W30 will work if that's all you can find, but small engines generally last longer with the straight 30W (dinosaur squeezings or synthetic).
Straight weight oil lubricates better. I’m considering synthetic for the rider mower and just changing it once a season.