Never said it would hurt your motor...
but i reiterate it doesn't take much to foul a sensor, may not kill it but it will not read correctly, affecting driveability, mileage and emissions. We have to use special silicon sealer that wont harm the O2 sensor on intake manifolds, even high sulfer fuel can damage the fuel level sender, I can tell when they change from summer fuel to winter fuel by customer complaints, being at the dealership I see the cars that no one else can fix as well as newer cars that are still under warranty, I have been dealing with obd2 for 10 years, the computer expects fuel that has certain characteristics, give it something else and it gets confused. sorry for the rant but in closing, if you do dump your old fuel in your car and it acts up later, be good enough to fess up to your mechanic, it will make his job a lot easier, or rent a car and put it in that. ;D SEP. Tim