This study presents an experimental stack-level thermal and hydrodynamic assessment of a model air-cooled PEM fuel cell. To mimic the heat generation inside the MEA, rubber heater films are used. Pressure drop along the stack channels and temperature distribution on the bipolar plate surface are measured for the channel Reynolds number range of 200-500 and the stack input power range of 100-250 W. Tests are performed with and without gas diffusion layers (GDL) to investigate the effect of GDL and its surface characteristics on the pressure drop and heat transfer. Our results indicate that, with the existing length of bipolar plates, a major part of plate minichannel is filled with the developing region. This leads to a higher heat transfer rates, thus more uniform stack temperature can be obtained with the penalty of higher fan power. The minimum measured temperature difference is about 10 °C and the values become more pronounced when the Reynolds number decreases. The existence of the GDL is observed to have negligible effect on the pressure drop.