PEM fuel cells are considered to be viable alternatives to Internal Combustion Engines (ICEs) in automotive applications due to their many advantages. However, one of the challenges is the need to remove considerable heat at relatively low temperatures (i.e. similar to 60-80 degrees C). Nanofluids may offer a promising solution to help reduce the size of thermal management part of PEM fuel cell systems. This paper describes a simulation model developed to theoretically study the effect of using of nanofluids as coolants on the size of the heat exchanger (HE) and the pumping power in PEM fuel cell cooling systems. Considering a 2.4 kW PEM fuel cell, 50/50 water-ethylene glycol based nanofluids with concentration of 0.05-2 vol% have been investigated. By using 0.05 vol% concentration, similar to 21% reduction of frontal area of the HE is obtained compared with that using the base fluid at constant coolant mass flow rate. By increasing nanoparticle concentration from 0.05 to 2 vol%, a further reduction of only similar to 4% of the frontal area of HE can be obtained. No significant difference was found in pumping power when using nanofluids compared that using the base fluid. Using standard models there is negligible differences in the thermal performance using a variety of nanofluids. (C) 2016 Elsevier Ltd. All rights reserved.