Cooling apparatuses and methods are presented for facilitating dissipation of heat generated by one or more electronic components. The apparatuses include, for instance, a coolant-cooled heat sink and a thermostat-controlled valve. The heat sink includes one or more coolant-carrying channels and one or more valve wells intersecting the channels. The thermostat-controlled valve is disposed, at least partially, within a respective valve well so as to intersect a respective coolant-carrying channel, and includes a valve disk and a thermal-sensitive actuator mechanically coupled to rotate the valve disk. The valve disk is rotatable between an open position where coolant is allowed to flow through the respective coolant-carrying channel, and a closed position where coolant is blocked from flowing through the respective channel. The actuator rotates the valve disk between the open position and the closed position, dependent on heating of the thermal-sensitive actuator by the electronic component(s).