In the field of rubber injection molding, pressures up to 3.000 bar and shear rates up to 10.000 s-1 are typical. Due to their nature rubbers are rheologically highly complex and show high viscosity levels in processing relevant shear rates. As a logical consequence high pressures occur during rheological experiments and therefore rubbers are subject to viscous dissipation [1]. This study is concerned with the different methods of calculating viscous heating, namely an improved method from Agassant [2] and 3D non-isothermal simulations with the injection-molding simulation software SIGMASOFT. For SBR and NBR viscosity was measured at 7 different shear rates und 3e temperatures. Each rheological experiment war simulated considering shear and elongational viscosity. The calculated average values for the temperature increase due to viscous dissipation were used for temperature correction of viscosity. Simulations showed, that the temperature varies around 20 °C throughout the cross-section. Therefore, temperature correction is clearly inevitable in order to provide reliable viscosity curves. The deviation between temperature corrected and non-temperature corrected viscosity values can easily be 30% and more. REFERENCES 1. Mitsoulis E. et al.(2017), Flow behaviour of rubber in capillary and injection moulding dies, Plastics, Rubber and Composites, 46:3, 110-118M. P. Brown and K. Austin, Appl. Phys. Letters 85, 2503–2504 (2004). 2. J.-F. Agassant, Polymer Processing: Principles and modeling, Hanser, (1991)