The major objective of the present study is to experimentally investigate the thermophysical properties and heat transfer capability of ZnO- and MgO-engine oil nanofluid as a coolant and lubricant in various engineering applications. The viscosity and thermal conductivity measurements have been performed at different temperatures (ranging from 15 degrees C to 55 degrees C) and solid concentrations (ranging from 0.125% to 1.5%). The nanofluids showed Newtonian behavior over the studied range of temperatures, and solid concentrations. Furthermore, the results revealed that the samples containing ZnO cause more increase in the dynamic viscosity compared to the samples containing MgO. The thermal conductivity has also been measured over the same range of temperatures and solid concentrations. The maximum enhancement of just over 28% and 32% at the temperature of 55 degrees C and the solid concentration of 1.5% has been observed for the ZnO- and MgO-engine oil nanofluid, respectively. Furthermore, the heat transfer performance of the nanofluids has been evaluated based on different figures-ofmerit, and it is revealed that using the MgO-engine oil nanofluid is advantageous just in laminar flow regimes while the ZnO-engine oil nanofluid would be advantageous in a limited range of temperatures. (C) 2018 Elsevier B.V. All rights reserved.