What do letters like SF, SH, and SJ mean on oil cans...and which one should I be using?

Dear Car Talk

Dear Car Talk | Dec 01, 1998

Dear Tom and Ray:

I was wiping the cobwebs off of my owner's manual for my '85 Chevy Caprice, and
it happened to fall open to the page about oil changes. It says I should use an
oil that has an API designation of SF. The oils I've been using, however, have
been designated SH and SJ. Am I doing my engine any harm? -- Basil

RAY: Absolutely not, Basil

TOM: The ratings are performance specifications for the oil. Basically, the
higher the second letter, the better the oil.

RAY: SJ is currently the top of the line, but you may still see both SH and SI
on store shelves. When a new designation appears, it just means that the
standards have been raised, and the new oil (in this case, SJ) meets those
higher standards.

TOM: The reason the standards keep going up is not due to some noble pursuit of
divine lubrication. It's because engine manufacturers are trying to meet
increasingly stricter government regulations for fuel economy and emissions. And
improving engine lubrication is one way to help meet those standards.

RAY: So SJ oils may have higher standards for viscosity, volatility, deposit
control and filterability, among other "oily" properties.

TOM: When your Caprice was built in 1985, SF was as good as it got. But it never
hurts to use better oil than you need, so anything above SF is fine for you.

RAY: By way of comparison, when my brother's '63 Dodge Dart was made, they
weren't even using letters yet for oil designations. All it said was "Caution:
Do Not Use Whale Blubber in Crank Case."

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