Reliable viscosity data within a wide range of shear rates are of crucial importance for the simulation of rubber injection molding. Due to the numerous user-specific compounds with varying formulations, no viscosity database is available and subsequently, viscosity measurement for rubber compounds has to be carried out very carefully to enable reliable simulation results. Slit die rheometry which is well known since the early 70th of the last century allows for improving pressure detection, widening the shear rate range to be covered and detecting wall slip effects. Adapting slit die systems to rubber injection molding machines offers new possibilities in rheological characterization of compounds with complex rheological behavior, performing measurements at pre-shearing conditions close to processing. Filler-filler interactions (Payne effect) strongly influence viscosity data which can be shown by RPA measurement at suitable pre-shearing conditions preventing material degradation. In this study NBR, SBR and FKM rubber compounds were characterized with a rubber process analyzer (RPA), a high pressure capillary rheometer (HPCR) and a special injection molding machine rheometer (IMMR) which allows shear viscosity measurements up to high shear rates for rubber compounds containing curatives. Viscosity data measured with RPA (conventional, pre-sheared) will be compared with data from HPCR and IMMR. The rheological evaluation of measured values and the approximation of true viscosity curves at higher shear rates take into account the temperature rise due to viscous dissipation. The importance of the temperature correction method is demonstrated for medium and high shear rates showing measured steel and wall temperatures in the rheological slit-die as well as presenting simulation results for the non-isothermal temperature field in the rheological slit. Finally the measurement of pressure dependency of viscosity will be shown for a SBR compound containing curatives.