Average amount of warm gas M_warm over time for all simulations with (blue) in comparison to all simulations without (orange) a given CR transport mechanism. Average masses for full-physics simulations are shown in grey. Shaded areas denote the minimum to maximum M_warm at a given point in time for all simulations in a given bin. Only CR heating by the streaming instability has a significant impact on the evolution of the warm gas in the cluster, and only after t > 1.5 Gyr.