API SP, ILSAC GF-6A, Dexos1 Gen 3: what the letters on the oil jug mean

Who writes the rules

Three groups set the standards you will see on a jug sold in the United States:

• API, the American Petroleum Institute, runs the licensing program that puts the "donut" and "starburst" symbols on the label. Its gasoline-engine categories are two letters starting with S: SN, SN Plus, SP.
• ILSAC, a committee of American and Japanese automakers, sets the GF series (GF-5, GF-6A, GF-6B). ILSAC categories add fuel economy requirements on top of the API tests.
• Individual manufacturers publish their own approvals when they want something stricter or specific to their engines. GM's is Dexos. Ford, Chrysler, and the European makers have theirs. If your manual names one, it overrides everything else.

API SP

SP became the current gasoline category in May 2020, replacing SN Plus. It was written for the engines that had become common by then: small, turbocharged, direct-injected, and running very thin oil to save fuel. Those engines produced three problems the old tests did not catch:

1. Low-speed pre-ignition (LSPI). In a turbocharged direct-injection engine under load at low RPM, the fuel-air mix can ignite before the spark. The resulting pressure spike can crack a piston. Certain additive chemistries make it more likely, so SP oils are formulated to prevent it.
2. Timing chain wear. Soot from direct injection ends up in the oil and grinds at the timing chain. A stretched chain throws off valve timing and is an expensive repair. SP adds a chain wear test.
3. High-temperature deposits. Turbochargers and hot-running pistons cook oil into varnish. SP tightens the piston deposit and oxidation limits.

SP is backward compatible. It is fine in any engine that called for SN, SM, SL, or earlier. An older engine gets a better oil than it was designed for. There is no downside.

ILSAC GF-6A and GF-6B

GF-6 launched alongside API SP and covers the same engine tests plus fuel economy. It comes in two flavors, and the letter matters:

• GF-6A covers the common viscosities: 0W-20, 5W-20, 5W-30, 10W-30, and similar. It is backward compatible with GF-5 and earlier. The starburst symbol on the front of the jug means GF-6A.
• GF-6B is only for 0W-16, a very thin oil a handful of newer Toyota and Honda engines specify. It is not backward compatible and gets a different symbol (a shield) so nobody puts it in an engine that wants thicker oil by mistake.

For nearly every vehicle on the road in Iowa, GF-6A is the one you want to see.

Dexos1 Gen 3

Dexos is General Motors' own approval, required for GM gasoline engines since roughly 2011 and printed on the oil cap of every recent Chevrolet, GMC, Buick, and Cadillac. GM runs its own test program and licenses oils that pass, and only licensed oils can carry the Dexos name and license number on the label.

Dexos1 Gen 3 took effect for licensed products in 2021. It goes further than API SP on the same problems: a stricter LSPI test, tougher limits on oxidation and thickening, and a turbocharger deposit test that simulates a hot turbo coking the oil. An oil that passes Dexos1 Gen 3 has passed a harder exam than API SP alone, which is why many non-GM owners look for it as a quality signal even though their manual does not require it.

If your GM vehicle is under warranty, using a Dexos-licensed oil is part of keeping it. The receipt should show an oil that carries the Dexos license.

What about viscosity?

The specification tells you the oil's quality. The viscosity grade, 0W-20 or 5W-30 and so on, tells you its thickness, and it comes from your manual, not the jug. The number before the W is cold-flow performance (lower is better in a Cedar Rapids January). The number after is thickness at operating temperature. Use what the manufacturer specifies. A quality oil in the wrong grade is still the wrong oil.

How to check what your engine needs

1. Look at the oil filler cap. Most manufacturers print the viscosity there, and GM prints the Dexos requirement.
2. Check the maintenance section of the owner's manual for the specification (API SP, GF-6A, Dexos1, or a manufacturer code).
3. Match both to the back label of the jug. Look for the API donut with "SP" in the top half, the ILSAC starburst, and if you drive a GM, the Dexos logo with a license number.

What we put in your engine

Oil To Go carries one full synthetic, made by Highline Warren, licensed to API SP, ILSAC GF-6A, and Dexos1 Gen 3. It covers what the overwhelming majority of vehicles in the metro call for, in the grade your manual specifies. European makes with their own approvals (BMW, Mercedes, VW, Audi, Volvo) need a different oil, which we quote separately when you book.