A radiator test system was developed to test the heat transfer performance of automobile radiators for various engine coolants. The system was made up from a circulation pump, coolant reservoir, axial fan, electric heaters, PLC controlled drivers and instruments for various mechanical measurements along with the tested radiators. Two different radiators, namely round and flat tube ones, and four different engine coolants, namely water, ethylene glycol, their 50/50 mixture and a commercial heat transfer oil, were tested. The experimental heat dissipation rates of the radiators were evaluated under a broad range of operating conditions. The air speed was changed between 2 and 4 m s-1, the coolant flow rate was varied between 0.1 and 0.3 l s-1, and the air temperature at the inlets of the radiators was changed between 25 and 35 °C, while the coolant temperature was fixed at 90 °C in all tests. The flat tube radiator dissipated on average 4.8% more heat than the circular tube one for water coolant, while it rejected on average 66.4% more heat than the circular tube one for ethylene glycol. Furthermore, when the heat transfer oil was used as coolant, the flat tube radiator dissipated on average 101.6% more heat than the circular tube one.