Abstract: An on-board motor vehicle fuel treatment system for a vehicle having primary and secondary fuel tanks, includes a discrete reservoir for liquid fuel supplement, an electrically powerable constant volumetric displacement pump, a transfer line having a suction line connecting the reservoir to the pump and a delivery line connecting the pump to the tanks, a check valve in each of the suction and delivery lines, a selector valve in the delivery line for normally connecting the pump to the primary tank and alternatively connecting the pump to the secondary tank, a normally open pump switch, an adjustable timer for maintaining the pump switch closed for a duration of time has a timer control for basing time duration on the basis of untreated volumetric units of fuel, and a switch for starting the timer and adjustable time duration for each volumetric unit on the timer control; the timer controlled pump switch is wired in series with the pump and a normally open selector valve switch is wired in series with the pump