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At this moment I’m changing the oil in my 2002 Toyota Tundra. While re-filling with fresh oil that I bought yesterday (Toyota API SL, SAE 5W-30) I grabbed an half-filled quart from the shelf from when I changed the oil about 7 months ago. The label on the bottle says "API SL, SAE 5W-30.

So what’s the difference between SL and SM?

Will the next oil I buy be SN?

Just curious

Correction! I meant to write that I’m currently filling with API SM, SAE 5W-30.

Is there a way to edit posts?

It is a rating system From the American Petroleum Institute. The Second letter “L,M” and yes probably soon “N” service categories. The First letter “S” is for gasoline, spark ignition engine the other is “C” for diesel compression ignitions. You can get a much better explanation than I can give at:

Thanks for the link!

Essentially the difference is the phosphorus and zinc levels. SL had higher allowances.

Phosphorus is poisonous to your catalytic converter. It’s a policy thing. You can be processing more phosphorous through your engine (having some percentage volatilizing and poisoning your cat) by changing SM too often. It’s a policy thing since if you’re changing it too often, you’re poisoning it less than you were at higher additive levels.