In this paper we report on an experimental study conducted on the thermo-electrical performance of a small-scale (i.e. 2.4 kW) Proton Exchange Membrane Fuel Cell (PEMFC), in which both conventional 50/50 water-Ethylene Glycol (EG), and 50/50 water-EG based ZnO nanofluids were used as coolants. PEMFCs are a promising alternative to Internal Combustion Engines (ICEs) for automotive applications. However, among other challenges, the large-sized cooling system of PEMFCs (i.e. the radiator) imposes a great challenge for this application. Using nanofluids as coolants has the potential to address this challenge. Employing selected nanofluids as coolants, with maximum 0.5 vol% nanoparticle concentration, showed no change in the electrical power outputs of the stack based on its polarisation curve, whereas the cooling capacity of the system was improved 29% compared with that while using 50/50 water-EG as coolant. The experimental investigation reported here confirmed the earlier theoretical finding that the frontal area of the radiator (i.e. used for fuel cell cooling) could be reduced by about 27% when nanofluids (0.5 vol%) replaced conventional EG/water coolants. Using 0.5 vol% ZnO nanofluid also showed just less than 10% increase in the pumping power compared to when the conventional 50/50 water-EG was used as coolant. It is concluded in this study that up to 0.5 vol% ZnO nanofluid can be applied to the PEMFC cooling system without affecting any electrical performance of the system. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.