In this study, an experimental analysis was used to measure the thermal conductivity (k(nf)) of WO3-MWCNTs/Engine Oil hybrid nanofluids, and a new significance was established. The preparation of nanofluid with a two-step method was achieved through the suspension of WO3 nanoparticles and MWCNTs in engine oil using ultrasonic waves. The diameter of the WO3 nanoparticles is in the range of 23 to 65 nm and the diameter of the MWCNTs in the range of 20 to 30 nm. According to the results, the k(nf) grows as the temperature and volume fraction of nanoparticles (phi) goup. Of course, the phi has a more significant influence on the k(nf), compared to temperature. Also, the maximum amount of k(nf) of hybrid nanofluid was at T = 60 degrees C and Phi = 0.6%, which increased by 19.85% compared to the base fluid. At last, two mathematical models for assessing knf were introduced. (C) 2020 Elsevier B.V. All rights reserved.