Convective turbulent-flow heat transfer experiments were performed with Therminol 59-based nanofluids containing copper nanoparticles at particle volume concentrations of 0.50% and 0.75%. These nanofluids have the unusual properties of being significantly above the thermal conductivity predictions of the effective medium theory with high dynamic viscosities. The friction factors and heat transfer coefficients of the nanofluids were experimentally determined and compared to the predictions from the standard correlation equations. The experimental heat transfer coefficient enhancements were also compared to the predicted heat transfer coefficient ratios of the nanofluids over the base fluid using their thermophysical properties. Finally, based on the measured thermophysical properties and heat transfer coefficients of the nanofluids, the effect of elevated temperature on the heat transfer coefficient ratios of the nanofluids over the base fluid were evaluated. (C) 2013 Elsevier Ltd. All rights reserved.