Can oil be put in a gas tank?

While a small amount of oil, diluted with a full tank of gasoline, does not harm the engine, it is not wise to add oil to a gas tank. Too much oil can do significant harm to the fuel system.

Many people have a small amount of a gas-oil mixture left over by autumn, because they are no longer using the lawn equipment that uses that mixture. As long as there is no more than a gallon or two of the mixture, and if the tank is already mostly full of gasoline, it is all right to add it to the tank.