In the manufacture of plastic components, predicting cooling duration and temperature distribution are critical for maintaining optimum productivity costs and part quality. We investigated the cooling cycle of injection molding for cylindrical shaped plastic components. A numerical model was formulated using the full conservative form of the energy equation with temperature dependent polymer properties having continuous equations of state. The cooling time predictions from this numerical method were in good agreement with our experimental results. This model predicted shorter cooling times than the often used non-conservative heat conduction model that uses constant polymer properties or a temperature dependent thermal diffusivity. Good agreement in cooling time was obtained using the model of Ballman and Shusman and the conservative model for part thicknesses #3 mm. The investigation indicated that the statistical cooling time model of Busch et al. is more suitable for predicting plastic part cooling.