Experimental investigations are carried out for the determination of transient heat transfer coefficients between parallel co-rotating and concentrically stationary disks with internal heat generation. The experimental model simulates a typical induction motor with unequal losses in the stator and rotor at the start-up condition. The data collected cover a range of Taylor numbers for various heat inputs. Quantitative assessment is made for the increase in heat transfer with speed of rotation under free convective ambient conditions. Temperatures along the axial, radial and tangential directions are measured. Unsteady heat transfer coefficients to the ambient air are evaluated in the radially diverging section. The results of the corresponding R-C network are obtained on a digital computer. The predicted values of temperatures at the corresponding nodal points are compared with the measured values and found to be in good agreement. The results are potentially very useful in the thermal design of electrical machines, more specifically, radially ventilated induction motors.