In this study many experimental measurements were conducted to examine the efficacy of loading MWCNT-TiO2 into SAE 20 W-40 on thermal conductivity (k). Through applying FESEM and XRD tests, molecular structures of nanoparticle were inspected and using two-step method, nanofluid samples at 0.1, 0.2, 0.4 and 0.8 vol% were prepared. After passing DLS and zeta potential tests, k(MWCNT-TiO2/SAE20W-40) was measured using KD2 Pro at 20-70 degrees C and 0.1-0.8 vol%. Based on results, it was observed that k(MWCNT-TiO2/SAE20W-40) was higher than k(SAE20W-40) and therefore inserting MWCNT and TiO2 into 20 W-40 has a positive effect on thermal conductivity up to 24.42%. Therefore, the number of dispersed nanoparticles has a considerable effect on k(SAE 20W-40) so that at 0.1 and 0.8 vol%, it was improved by 3% and 24.42%, respectively. Although k(SAE 20W-40) declines by 5.75% with increasing temperature from 20 to 70 degrees C. (C) 2021 Elsevier B.V. All rights reserved.