You left out the other convenient part: read the manufacturer’s limited warranty booklet: Failure to use “recommend” fluids may result in engine damage not covered under warranty. The onus is on you, not them. You incorrectly applied the Magnuson Moss Warranty Act here. DEXOS is a standard, not a product. It does not apply in this situation
Failure to use recommended or equivalent oils, may result in damage.
Please read their statement.
When choosing oil for your vehicle, you should always look or ask for API-licensed oil. API has made it easy to find these oils: licensed oils display one or both of the API motor oil quality marks—the API Service Symbol "Donut" and the Certification Mark "Starburst." These marks are part of API's Engine Oil Licensing and Certification System (EOLCS), a voluntary licensing and certification program that authorizes engine oil marketers meeting API requirements to display the API quality marks. - API.
GM can only legally require you to utilize an API approved product. They can “recommend” to use a Dexos product. However they cannot require you to pay them a licensing fee, to use their engine oil. Period, end.
Section 102(c),
15 U.S.C. 2302(c), prohibits tying arrangements that condition coverage under a written warranty on the consumer's use of an article or service identified by brand, trade, or corporate name unless that article or service is provided without charge to the consumer.
Meaning, GM cannot legally require you to buy a Dexos branded product. They can only give it to you for free then.
That’s the law. GM can require you to use a generally available replacement wear item part. If you use autozone brakes, and your transmission goes out: They cannot void your transmission warranty.
If you put Michelin tires on your car instead of Goodyears, they cannot void your warranty if your engine blows up.
They can require you to use DOT approved tires. They can require you to use an API certified oil.
It’s also on them to prove, that the engine oil caused the damage.
