of injector deposits, ring sticking, and the incompatibility with conventional lubricating oils. As the viscosity represents one of the important parameters characterizing the deterioration of oil, optimizing the suitable range of viscosity of fuel oil is required to satisfy the biodiesel specifications of different countries [9]. Thailand specifies a 3.5–5 mm2 s1 standard for biodiesel [10]; however, biodiesel produced by communities for agricultural machinery have a regulated viscosity of 1.9–8mm2 s1 at 40C [11].