Methanol, benzine, benzol, naphtha, kerosene, and any other volatile, flammable, or combustible liquid suitable for use as a motor fuels blending agent or fuel expander shall be exempt from the taxes imposed under sections 66-489, 66-489.02, 66-4,105, 66-4,140, 66-4,145, and 66-4,146 unless and until such methanol, benzine, benzol, naphtha, kerosene, or other blending agent or fuel expander is blended with motor fuels or placed directly into the supply tank of a licensed motor vehicle. Any person blending such products with motor fuels or placing such products into the supply tank of a licensed motor vehicle shall pay the taxes imposed under such sections directly to the department on forms provided by the department at the same time as the motor fuels with which it is blended become subject to taxation or, if the tax imposed on the motor fuels has already been paid, upon blending. The taxes imposed by this section shall not apply to fuel additives which are used to enhance engine performance or prevent fuel line freezing or clogging when placed directly into the supply tank of a motor vehicle in quantities of one quart or less.