One of the key reasons for the failure of lube oils is their thermal degradation owing to elevated heat conditions in vehicle engines. In this study, the thermal degradation studies of the lube oils were performed using a simultaneous thermal analyzer (TGA/DTG/DSC). Furthermore, the engine thermal efficiency was determined experimentally using an AVL dynamometer under different operating conditions. TGA results showed that the oxidation onset temperature and burnout temperature of Al2O3/TiO2 hybrid nanolubricants could be delayed by 54.9 degrees C and 38.7 degrees C, respectively, as compared with the reference oil (5W-30). Comparing the engine results, the Al2O3/TiO2 nanolubricants presented enhancement of heat transport characteristics and brake thermal efficiency by 9-14% and 3.9-8.6%, respectively, compared with the reference oil. Hence, the high thermal stability of Al2O3/TiO2 nanolubricants allows to be used in a wide temperatures range with a higher fuel economy, optimize lube oil drain intervals and reduce maintenance costs in vehicles. (c) 2019 Elsevier B.V. All rights reserved.