A temperature scanning rotational viscometer and visualization techniques are utilized to evaluate the viscosity behavior of kerosene-based jet fuels from -20 degrees C to sample cloud point temperatures. The uncertainty of using the rotational viscometer technique is evaluated and determined to be acceptable. The rotational viscometer is used to perform shear rate studies on JP-8, Jet A, and JP-8 blended with a low-temperature additive designed to improve fluidity. Clouding of the neat fuel samples during cooling, visualized in a unique optical cell using cross-polarized light and a He-Ne laser, was determined to not cause non-Newtonian viscosity behavior. Polarized light is used to demonstrate that neat fuel clouding during cooling is likely due to free droplets of a water/di-ethylene glycol monomethyl ether (water/DIEGE) mixture, while clouding of the jet fuel/additive blend was caused by crystallization. Viscosity results are presented for all jet fuel samples. Selected results are compared with viscosity measurements obtained from other methods and are determined to be in good agreement. Complex non-Newtonian viscosity behavior, including both pseudo-plasticity and dilatancy, was identified for the fuel/additive blend. Viscosity results and the effects of shear rate changes matched observed solidification behavior.