what gas is better
does it hurt the car to put regular unleaded 87 octane in a car that is flex fluid or can you
use both. some one says less mileage with flex fluid, But the per
Correct. That is why it is called flex fuel. You will get better fuel mileage as the methanol decreases in the fuel, but it looks like we are stuck with a 10 percent mix minimum in today's fuel. My neighbors rig is a flex fuel, and during a trip he tried E85 for 1 tank and said never again, his mileage dropped horribly and the power was nonexistent.
If your vehicle is rated for E85 you can use it, but you are better off switching when the tank is almost empty. You will lose 15-20% fuel economy, so if the E85 isn't that much cheaper then stick with regular gasoline. If your car is not rated for E85 then putting it in will turn on a bunch of emissions and warning lights.
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