If I was going to dilute the gasoline with anything I would try an E85 blend.  However, our gas tank at the farm was filled full of diesel fuel by the distributer, we wound up with about 60% gasoline and 40% diesel in the tank.  Our three Oliver 77 were the only thing that would burn the stuff, and they really smoked black.  The distributer wound up paying to repair and tune up all of our vehicles, and the plugs where pretty black as well.