Crude biodiesel was proven as a cosolvent in the methanolysis of sunflower oil catalyzed by calcined CaO. This reaction was modeled and optimized statistically in terms of reaction temperature (33.2-66.8 degrees C), methanol-tooil molar ratio (3.5:1-8.5:1) and catalyst concentration (0.219-1.065 mol/L). The cosolvent loading was 10 wt% (based on oil weight). The optimum reaction conditions were found to be: the methanol-to-oil molar ratio of 7.1:1, the catalyst concentration of 0.74 mol/L and the reaction temperature 52 degrees C, ensuring the best esters content of 99.8%, for the reaction time of 1.5 h, which is close to the reported experimental value of 98.9%. Also, the used catalyst was recycled with no additional treatment in the further four consecutive cycles under the following reaction conditions: methanol-to-oil molar ratio 6:1, the concentration of catalyst 0.642 mol/L (only in the first run), the reaction temperature 50 degrees C, cosolvent-crude biodiesel loading 10 wt% to oil weight. The second recycling reaction provided the highest FAME content of 97.7% after 5 h.