Usability of a waste vegetable oil in coated diesel engines was experimentally investigated. Waste corn oil was blended with petroleum diesel fuel by ratios of 15% corn oil to %85 diesel fuel (815), 35% corn oil to %65 diesel fuel (B35) and 65% corn oil to %35 diesel fuel (B65). The surfaces of the engine piston and both intake and exhaust valves were coated with ZrO2 layer in order to make the combustion chamber insulated. Thus heat transfer through the combustion chamber was aimed to be reduced with the purpose of increasing the thermal efficiency and performance of the engine and also maintain the usability of vegetable oil in diesel engines. B15, B35, B65 and standard diesel fuels were used in the coated test engine. Performance parameters and exhaust emissions characteristics of all the above mentioned fuels were clarified and compared with uncoated engine test values of normal diesel fuel. It is believed that the main purpose of this study has been achieved as the engine performance parameters such as power and torque of the engine were increased with simultaneous decreases in the brake specific fuel consumption (bsfc). Besides, many of exhaust emission parameters such as CO, HC, and smoke opacity were decreased. (C) 2012 Elsevier B.V. All rights reserved.