In this study, two oxygenated fuels consisting of butanol and diethyl ether (DEE), both possess same number of carbon, hydrogen and oxygen atom but difference functional group, were blended with the waste plastic pyrolysis oil to use in a 4-cylinder direct injection diesel engine without any engine modification. In addition, the effect of castor oil addition to such fuel blends was also investigated. Four tested fuels with same oxygen content were prepared for engine test, comprising DEE16 (84% waste plastic oil blended with 16% DEE), BU16 (84% waste plastic oil blended with 16% butanol), DEE11.5BIO5 (83.5% waste plastic oil blended with 11.5% DEE and 5% castor oil) and BU11.5BIO5 (83.5% waste plastic oil blended with 11.5% butanol and 5% castor oil). The results found that the DEE addition to waste plastic oil increased more emissions than the butanol addition at low engine operating condition. However the benefit to reduce CO and smoke was observed when the DEE blend was tested at high engine operating condition compared to the butanol blend, while HC and NOx was similar. The fuel blend with the combination of DEE and castor oil showed a more advantage to decrease HC, CO, NOx and smoke emissions at both engine operating conditions tested.