For injection molding of rubbers, the bulk material temperature at cavity entrance of rubber compounds is critical to the subsequent curing reaction. Currently, all commercial process simulations employ the initial material temperature as constant. However, the actual bulk temperature can greatly differ from the desired set point, as it depends on shear energy input by the screw, back pressure and energy flow by heat conduction. Thus, a strong axial (and radial) temperature profile of the material in the screw antechamber can occur. In this work, the axial temperature profile is characterized, and models for its dependence on key machine parameters are derived. To do so, a Central Composite Design of Experiments (CCD), where the effects of dosing speed, back pressure and cylinder set temperature are taken into account, is conducted and analyzed. The injection molding equipment consists of a rubber injection molding machine, and a specially designed test set-up to measure the bulk temperature. This device is mounted on the moveable clamping plate of the injection molding machine, which facilitates the exact lateral positioning of a thermocouple pin in the screw antechamber. The investigated material is and carbon-black-filled NBR rubber compound. Two batches of this compound, differing in their storage prehistory, are used for the characterization. A temperature inhomogeneity of several degrees centigrade was measured for both compounds. By means of statistical analysis, it was possible to derive key dosing factors and to quantify their influence on the axial temperature. The deviation of the mean bulk temperature as well as the shape of the axial temperature profile will be discussed. Finally, the differences between the two NBR batches due to storage effects will be demonstrated.