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Floyd County, Iowa | Short answer is SJ is an older rating.
SM is newer rating than SJ. It goes alphabetical.
SN is newer than SM.
You can use SM or SN in older machines that called for SJ, but shouldn't use SJ oil in newer machines that call for SM or SN.
The SJ rating isn't made any longer, from what I can find.
Here's a link to explain it better than I could type it.
https://www.api.org/products-and-services/engine-oil/eolcs-categorie...
I'm pretty sure that your "plain old 10w30" has an API rating in that little circle on the back of the jug. I've never seen oil that didn't have a rating on it.
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Edited by oldbones 4/8/2026 18:39
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10w30 vs 10w30 SJ
