Zirconia (ZrO₂) and silica (SiO₂) nanoparticles suspended in water are the focus of this investigation on the influence of environmental variables on the dynamic viscosity of these nanofluids. Two different viscometers (a falling ball and a capillary) were used to measure the range of temperatures from 30 to 60 °C and the percentage of particles from 4 to 15.4%. The results demonstrate that, similar to their base fluids, nanofluids’ viscosity reduces as temperature rises. Surfactants are added to nanofluids to improve their stability at room temperature; however, this is likely at the expense of an increase in viscosity. However, the modified Krieger-Dougherty relation provides reasonably accurate estimation of nanofluid viscosity within a narrow limit of solid size of particle to cumulative size, while relations attained from the lenient liquid concept, like Einstein’s and Bachelor’s, fail to predict nanofluid viscosity for solid concentrations above 1.5 wt.%.

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