Using vegetable oils as fuel for diesel engines in the long term may cause some extremely serious problems, such as an increase in toxic emission and pollutants, reduction in engine power, and degradation of lubricating oil (LO) due to deposit formation, abrasion, and wear, as well as damaged engines. In this study, the 4 stroke-4 cylinder-Yanmar TF120M diesel engine was tested the endurance during 300 h on diesel fuel (DF) and preheated straight jatropha oil to evaluate the effects of these two fuel types on the degree of deposit formation, LO, brake-specific fuel consumption (BSFC), and emission characteristics. The results showed that, although the properties of straight jatropha oil were improved by preheating at 90 degrees C (SJO90), the degree of deposit formation for SJO90 was observed higher in comparison with DF. Furthermore, scanning electron microscopy (SEM) was used to analyze the deposits. Related to engine performance and emission characteristics, higher BSFC, unburnt hydrocarbons and carbon monoxide emissions, and lower nitrogen oxide emissions for SJO90 compared to DF were presented. About the results of LO analysis, the excessive metal concentrations in LO of test engine for SJO90 were much higher than the case of using DF. Besides, an increase in LO density and a reduction in LO viscosity also showed the degradation of LO for SJO90 in comparison with DF after test time.