To improve part quality and consistency injection molders strive to control the temperature of the molten plastic during cavity filling. In-mold temperature sensors can effectively measure the temperature of the mold surface that contacts the melt; however, they do not provide a measure of the bulk melt temperature. An analysis was developed to use data from in-mold thermocouples to predict the plastic's bulk melt temperature. This analysis integrates the heat flux through the mold steel to calculate the bulk melt temperature. A mold instrumented with an in-mold thermocouple and an IR temperature sensor was used to validate the predictions. The effects of changing barrel temperature, coolant temperature, injection velocity, and cooling time were studied using a 21 run DOE. Validation was performed by comparing bulk temperature data from the IR temperature sensor with temperature predictions derived from the in-mold temperature sensor. Trends in the melt temperature were consistently predicted, however, the magnitudes were low due to residual heat remaining in the part at the end of the molding cycle. The analysis was more sensitive to process changes than raw data from the in-mold temperature sensor, thereby improving process observability.