A system for the slow purge of a fuel cell stack. A pump can be used to keep the coolant circulating, so that the stack, an associated radiator, and coolant plumbing therebetween are maintained at the same temperature. The heat from the stack, liquid coolant, and radiator can be used to provide the heat of vaporization of the liquid in the stack, and the liquid water can be removed from the stack as water vapor. Because the air flow rate is relatively low, there is sufficient time for the water to vaporize and for the air to come to the same temperature as the stack, which is also facilitated by high surface area for heat transfer. Purge air can be drawn into the stack through the radiator, via a purge air blower, which preheats the air to help avoid frigid air contacting the stack.