To improvement fuel characterislic of high viscosity Wastee oil, we preparea mixing fuel and used oil as dilute solvent. We observed layer separation, optimum mixing ratio, fuel characteristics. We kept on 3400~3600 rpm at mixing condition and tested it by temperature and time variation. To decrease kinematic viscosity and to increase exothermic quantity, we mixed light oil, buncker C oil, water and surfactant and showed probability of emulsion fuel oil. In the case of mixing fuel in waste oil buncker C oil/light oil/water, exolhermic qllantily as added water was observed 19% increases by 2:4:3:1 mixing ratio.