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 bio-diesel specifications of different countries [9]. Thailand specifies a 3.5–5 mm 2 s1 standard for bio diesel [10]; however, bio diesel produced by communities for agricultural machinery have a regulated viscosity of 1.9–mm s1 at 40C [11].