A data center cooling system includes a thermosiphon, an actuator coupled to the thermosiphon, and a controller. The thermosiphon includes an evaporator; a condenser; and at least one conduit coupled between the evaporator and the condenser to transport a working fluid between the evaporator and the condenser. The controller is coupled to the actuator and configured to operate the actuator to adjust a liquid level of the working fluid in the evaporator based, at least in part, on a parameter associated with a heat load of one or more data center heat generating computing devices.