Abstract In this work, a nanofluid based on multi-walled carbon nanotubes was formulated, and its heat transfer characteristics experimentally examined for turbulent flow in a straight tube. The experiments found that using the nanofluid resulted in an increase in pumping power and also a decrease in the observed convective heat transfer characteristics. This suggests that multi-walled carbon nanotube nanofluids in turbulent flows will actually impair heat transfer rather than improve it, and so may not be an appropriate heat transfer media in forced turbulent flows.