E15 is not flex fuel. E85 is what is considered flex fuel.My newer Kia(s) are quite clear to not use alcohol above 10%. I do not know if flex fuel would void the warranty but I would not test it.
My mother in laws Buick has a green gas cap and indicates that it will use flex.
Interesting, the gas cap on my 2022 F250 7.3 says E15. I run it frequently when Sheetz has a sale.That's funny because my 21' F350 7.3 godzilla says no more then 10% ethanol in the owners manual.
Thanks for the clarificationE15 is not flex fuel. E85 is what is considered flex fuel.