Global biodiesel production grew by 23% per year between 2005 and 2015, leading to a very strong expansion of the sector in a decade and, at the same time, the interest in the use of liquid biofuels/ biodiesel in compression ignition engines has grown quickly. Taking into account that the use of biodiesel in IC engines directly affects their coolant temperature, with impact on performance, in this study an experimental campaign has been carried out on a 4-strokes single cylinder engine, aimed to assess whether the use of nanofluids, instead of water, could be a valuable solution to reduce peak engine temperature. Such nanofluids were characterized by higher thermal conductivity compared to conventional fluids, due to CuO nanoparticles added at different concentrations within the base fluid. Measurements of temperature were recorded at steady and unsteady conditions, by proper thermocouples located around the exhaust valve seat in the cylinder head and in the exhaust valve spindle. Particularly, temperatures of the exhaust valve spindle and exhaust valve seat in the cylinder head were measured at part and full engine loads, using water as coolant and then CuO based nanofluids. Experimental results showed that, at 100% engine load in unsteady conditions, it was possible to achieve a temperature reduction up to 13.6% on the exhaust valve seat and up to 4.1% on the exhaust valve spindle, when nanofluid at 2.5% volume concentration was used. (C) 2018 Elsevier Ltd. All rights reserved.