Controlled Start Transmissions can be described as a mechanical transmission combined with a hydraulic clutch for controlled torque output. CSTs are commonly used to start up heavy loads for example mining conveyors and produces heat during startup. Models for CST clutch heat generation together with thermal behavior has been developed and investigated. This includes a temperature model together with a kinetic model of the gearbox and a torque model of the clutch. Validation of separate model components and sensitivity analysis of parameters are conducted. The developed models are then compared by analyzing measurements and simulations to investigate generated heat during regular usage.