500 h durability, performance and emission tests are conducted on a single cylinder high speed automotive diesel engine for the ethanol blended biodiesel fuel. Esterified cotton seed methyl ester of 5% by volume is mixed with 95% neat diesel to obtain the base biodiesel fuel (B5). The base fuel is mixed with 20% pure ethanol to derive the ethanol blended biodiesel fuel (B5E20). The parameters like blow-by, crank case pressure and lubricating oil consumption are experimentally investigated along with performance and emission characteristics for both the test fuelled engines. The result of these tests showed a significant loss in maximum brake power and maximum brake torque at the end of 500 h durability run when the engine is fuelled with B5E20. The lubricating oil consumption and positive crank pressure of B5E20 fuelled engine is comparatively higher than B5 fuelled engine during the durability trials. Reduction in smoke and CO emissions are noticed for B5E20 fuel over the entire range of speed whereas NOX and unburned hydro carbon emissions get decreased at lower to medium speed range and increases thereafter. As expected, all the engine emissions increase after 500 h of durability run for both the fuels. © 2019