Cooling system for fuel cell stacks (22, 26), the cooling system comprising: - at least a first cooling module, which comprises: - a fuel cell stack (22, 26) having at least one fuel cell, - a supply line connection (30, 34) for connecting a supply line (38, 42) for supplying cooling medium to the fuel cell stack (22, 26), - a drain line port (46, 50) for connecting a drain line (54, 58) for discharging cooling medium from the fuel cell stack (22, 26), - a vent line connector (94, 98) for connecting a vent line (102, 106), - at least a second cooling module comprising: - at least one collector line, the collector line being connected to the supply line connection (30, 34) of the at least one first cooling module via the supply line (38, 42) - at least one cooler line connection (126, 130) for connection to a cooler line (134, 138) of a cooler (118, 122), via which cooled cooling medium of the at least one fuel cell stack (22, 26) can be supplied to the collector line - at least one bypass line connection (142, 146) for connection to a bypass line (150, 154), by means of which cooling of the cooling medium can be bypassed - a startup heater which is connected to the collector line via a startup heater supply line and a startup heater discharge line, the startup heater supply line and the startup heater discharge line being arranged in the flow direction of the collector line downstream of a cooling medium supplied to the collector line via the bypass line connection (142, 146), and - at least one heat exchanger supply line port and at least one heat exchanger discharge line port for connecting a heat exchanger. - at least a first cooling module, which comprises: - a fuel cell stack (22, 26) having at least one fuel cell, - a supply line connection (30, 34) for connecting a supply line (38, 42) for supplying cooling medium to the fuel cell stack (22, 26), - a drain line port (46, 50) for connecting a drain line (54, 58) for discharging cooling medium from the fuel cell stack (22, 26), - a vent line connector (94, 98) for connecting a vent line (102, 106), - a fuel cell stack (22, 26) having at least one fuel cell, - a supply line connection (30, 34) for connecting a supply line (38, 42) for supplying cooling medium to the fuel cell stack (22, 26), - a drain line port (46, 50) for connecting a drain line (54, 58) for discharging cooling medium from the fuel cell stack (22, 26), - a vent line connector (94, 98) for connecting a vent line (102, 106), - at least a second cooling module comprising: - at least one collector line, the collector line being connected to the supply line connection (30, 34) of the at least one first cooling module via the supply line (38, 42) - at least one cooler line connection (126, 130) for connection to a cooler line (134, 138) of a cooler (118, 122), via which cooled cooling medium of the at least one fuel cell stack (22, 26) can be supplied to the collector line - at least one bypass line connection (142, 146) for connection to a bypass line (150, 154), by means of which cooling of the cooling medium can be bypassed - a startup heater which is connected to the collector line via a startup heater supply line and a startup heater discharge line, the startup heater supply line and the startup heater discharge line being arranged in the flow direction of the collector line downstream of a cooling medium supplied to the collector line via the bypass line connection (142, 146), and - at least one heat exchanger supply line port and at least one heat exchanger discharge line port for connecting a heat exchanger. - at least one collector line, the collector line being connected to the supply line connection (30, 34) of the at least one first cooling module via the supply line (38, 42) - at least one cooler line connection (126, 130) for connection to a cooler line (134, 138) of a cooler (118, 122), via which cooled cooling medium of the at least one fuel cell stack (22, 26) can be supplied to the collector line - at least one bypass line connection (142, 146) for connection to a bypass line (150, 154), by means of which cooling of the cooling medium can be bypassed - a startup heater which is connected to the collector line via a startup heater supply line and a startup heater discharge line, the startup heater supply line and the startup heater discharge line being arranged in the flow direction of the collector line downstream of a cooling medium supplied to the collector line via the bypass line connection (142, 146), and - at least one heat exchanger supply line port and at least one heat exchanger discharge line port for connecting a heat exchanger.