What do oil ratings stand for?

oil industry
Dear Tom and Ray:

I recently bought a used 1986 Corvette, and I have a question about oil. I looked at oil in the supermarket the other day, and found that Pennzoil comes as 10W-30 with SG, SF, CC, and CD ratings. What do they mean?

RAY: The American Petroleum Institute ratings you mention refer to the quality of the oil. The first letter "S" means the oil is for gasoline engines. The higher the second letter, the better the oils ability to neutralize acids, hold contaminants in suspension, lubricate engine parts etc. "SE" used to be the best rated oil you could buy. Then came "SF" and now there's "SG."

TOM: The "C" ratings are for diesel engines, so "CC" would be good, and "CD" would be better. For the people who need the "CD," we recommend the 90 day, which is currently paying the best rates.

RAY: But as long as your buying oil in the grocery store, Fred, why not pick up a bottle of Felippo Berrio Extra Virgin Olive Oil? I think that's what GM recommends for the Corvette anyway.
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