Present research deals with crude oil production from water hyacinth biomass and its biodiesel preparation. Alcohol additive n‐pentanol is mixed with biodiesel and diesel blends to identify their effects on diesel engine performance and emission parameters experimentally. Water hyacinth oil (WHO) is produced through Soxhlet extraction technique, and its biodiesel is prepared by transesterification. n‐pentanol is mixed through magnetic stirring in biodiesel‐diesel blends to improve their combustion quality and efficiency. Prepared fuel blends properties are examined as per ASTM standards. Experimental results reveal that, BSFC and BTE are evaluated as 0.26 kg/kW‐h and 29.5%, respectively, with HC emissions as 29 ppm, CO emissions as 0.28 vol%, NOx emissions as 330 ppm and CO2 emissions as 2.21 vol% for WHB20D75P5 fuel at maximum load. The comparison of D100 and WHB20D80 with respect to WHB20D75P5 reveals 3.27% reduction and 7.27% improvement in BTE, respectively. Both HC and CO are reduced by 14.70% and 22.22% for WHB20D75P5 fuel compared to diesel. NOx and CO2 emissions are increased by 6.79% and 12.75% for WHB20D75P5 fuel compared to diesel. Overall, WHB20D75P5 fuel is the best performer.