Abstract: A locomotive cooling system including a conduit adapted to conduct therethrough a flow of coolant; a power source providing a nominal voltage; and a valve assembly including a valve body defining a drain passage communicable with the conduit, a plunger movable between a closed position in which the conduit and the drain passage are separated and an open position in which the conduit and the drain passage are in fluid communication. A control assembly moves the plunger between the closed position and the open position. The control assembly, including a temperature sensor for detecting the coolant temperature, and connected to the power source. The control assembly opening the valve assembly when the system is either at a first threshold coolant temperature when the power source voltage is nominal or a second threshold coolant temperature when the power source voltage is low.