The three-pass turbulated serpentine channel has many applications in internal turbine blade systems. However, the studies on the effects of the outflow ratio are lacking, which decreases the thermal analysis accuracy in such a model. To fill this gap, outflow-ratio experiments are conducted on the Nusselt number distributions of a three-pass turbulated channel. The current experimental results can guide and optimize the turbine blade internal cooling system. The results show with the mass flow of the lateral outlet increasing, the low-heat transfer region on the lateral-outflow passage gradually expands. Increasing the mass flow of the lateral outlet heightens the spanwise-averaged Nusselt number of the lateral-outflow passage, especially under the static condition. In the lateral-outflow passage, the rotation significantly improves the Nusselt number uniformity, particularly at the high mass flowrate of the lateral holes; the rotation shows slight effects on the spanwise-averaged Nusselt number of the lateral-outflow passage at low rotation numbers, whereas the profound influence is observed for the spanwise-averaged Nusselt number under high rotation-number condition. The rotation can profoundly increase the pressure coefficient leading to a reduced pressure loss with the rotation number increasing from 0.03 to 0.06.