Oil-free turbomachinery have emerged as one of the core technologies for the future green power generation systems as stand-alone systems or hybridized with high temperature fuel cells or solar systems. Oil-free technology allows compact, clean, and maintenance-free operation, and foil bearings are at the center of the technology. Since their first commercial applications in the air cycle machines and auxiliary power units in 1970s, significant improvement has been made to the computational models for rotordynamic behavior. However, many technical issues still remain unsolved or poorly understood, and one of them is thermal management. This paper presents transient three-dimensional thermohydrodynamic (3D THD) model of radial foil bearings to predict transient thermal behavior of the bearing-rotor system. The transient model involves transient energy equations applied to all the mechanical structures and gas film. The model was verified through extensive experimental measurements of transient thermal behavior of three-pad foil bearing for various cooling air pressures, external loads, and speeds. The predictions showed very good agreements with the experiments, and also the 3D THD model could predict potential thermal instability observed in the experimental measurements.