
No, you should not use regular 87-octane gasoline in a car that is specifically designed and labeled as a Flex-Fuel vehicle (FFV) for E85. While the vehicle might run, doing so can cause significant and costly damage to the fuel system and engine over time. The core issue is that E85 (a blend of 85% ethanol and 15% gasoline) requires very different engine components and calibration compared to standard gasoline.
E85-compatible vehicles are built with hardened materials in the fuel system to resist the corrosive effects of ethanol. Using 87-octane gas in an E85 car bypasses these protections. Key components at risk include:
Using 87-octane in an E85 car will also void your powertrain warranty. While you can put E85 in a regular gasoline car (though it's not recommended), the reverse is far more dangerous for the vehicle's health. If you accidentally put 87 in your E85 car, topping it off with E85 to dilute the mixture is the best immediate action, but consistent use should be avoided.


