The effective temperature in rotor type curemeters is — according to DIN 53529 — controlled using an unfilled EPDM compound with dicumylperoxide as cross‐linking agent. The rate of DCP decomposition has a well‐known temperature dependence. This rate is also in all practical cases the same as the rate of cross‐linking. Therefore, the measured rate of cross‐linking indicates the effective temperature in the reaction cavity. The rotor in common curemeters is clamped. Because it can not be heated directly, this rotor is a heat sink in the cavity. The effect is a temperature gradient in the cavity depending on the heat conductivity of the tested compound. This temperature gradient in rotor type curemeters is compared to rotorless curemeters. It is shown that using the unfilled EPDM/DCP compound for temperature calibration leads to a too high effective temperature for filled compounds.