What could fail on the car and create multiple things on the car not to…
I accidentally filled up with flex fuel. Should I be worried, what should I do?
It can damage fuel lines, injectors, hoses and other rubberized parts, and cause engine startup problems, rough running and other ills. Flex fuel engines are modified to prevent those problems. The E85 Ethanol based fuel should be removed from the fuel tank ASAP if you tank was below 1/4 tank when you filled up.
If you only added a few gallons, I wouldn’t worry to much. Just drive it as normal and once it gets down to 3/4 of a tank, top it back off. Repeat for a week or so. This should be enough to help prevent any damage.