A surgical system, comprising: an ultrasonic surgical instrument, including: a waveguide defining a blade at a distal end thereof and a lumen extending through a portion of the blade, an inflow conduit disposed in communication with the lumen, the inflow conduit configured to supply fluid to the lumen, and a return conduit disposed in communication with the lumen, the return conduit configured to receive fluid from the lumen; and a cooling module, including: a pump assembly operably coupled to the inflow and return conduits, the pump assembly configured to pump fluid through the inflow conduit, into the lumen, and back through the return conduit for cooling the blade, at least one sensor (513, 515) configured to sense at least one of a property of the fluid pumped into the inflow conduit or a property of the fluid returned from the return conduit, and a controller configured to control the pump assembly according to the at least one sensed property, wherein the at least one sensor is configured to sense a temperature of the fluid returned from the return conduit, and wherein the at least one sensor is further configured to sense a temperature of the fluid pumped into the inflow conduit, wherein the controller is configured to determine a differential between the temperature of the fluid pumped into the inflow conduit and the temperature of the fluid returned from the return conduit and to turn the pump assembly off when the differential is below a threshold differential. an ultrasonic surgical instrument, including: a waveguide defining a blade at a distal end thereof and a lumen extending through a portion of the blade, an inflow conduit disposed in communication with the lumen, the inflow conduit configured to supply fluid to the lumen, and a return conduit disposed in communication with the lumen, the return conduit configured to receive fluid from the lumen; and a waveguide defining a blade at a distal end thereof and a lumen extending through a portion of the blade, an inflow conduit disposed in communication with the lumen, the inflow conduit configured to supply fluid to the lumen, and a return conduit disposed in communication with the lumen, the return conduit configured to receive fluid from the lumen; and a cooling module, including: a pump assembly operably coupled to the inflow and return conduits, the pump assembly configured to pump fluid through the inflow conduit, into the lumen, and back through the return conduit for cooling the blade, at least one sensor (513, 515) configured to sense at least one of a property of the fluid pumped into the inflow conduit or a property of the fluid returned from the return conduit, and a controller configured to control the pump assembly according to the at least one sensed property, a pump assembly operably coupled to the inflow and return conduits, the pump assembly configured to pump fluid through the inflow conduit, into the lumen, and back through the return conduit for cooling the blade, at least one sensor (513, 515) configured to sense at least one of a property of the fluid pumped into the inflow conduit or a property of the fluid returned from the return conduit, and a controller configured to control the pump assembly according to the at least one sensed property, wherein the at least one sensor is configured to sense a temperature of the fluid returned from the return conduit, and wherein the at least one sensor is further configured to sense a temperature of the fluid pumped into the inflow conduit, wherein the controller is configured to determine a differential between the temperature of the fluid pumped into the inflow conduit and the temperature of the fluid returned from the return conduit and to turn the pump assembly off when the differential is below a threshold differential.