The current paper added several kinds and amounts of nanoparticles into traditional engine oil to form a new type of cooling medium (nanofluids). Two interface-tracking methods (CLSVOF and Eulerian) were employed to discuss the transient flow and heat transfer of engine oil and nanofluids with different nanoparticles (copper and diamond) and volume concentrations (1%, 2% and 3%). The distributions of oil filling ratio and heat transfer coefficient were investigated at various crank angles. The advantages of nanofluids on cooling down the piston gallery were illustrated by comparing the statues of flow and heat transfer in local surfaces at the same moment (C) 2017 Elsevier B.V. All rights reserved.