An irrigation system having mobile towers interconnected by spans, a plurality of fluid conduits supported on or formed through the spans and connectable to a source of water, and a drive system for actuating movement or travel of the spans or towers. The fluid conduits may include orifices or sprinkler heads for dispersing water onto a field. The drive system may include a gearbox with gears and lubricant therein. The irrigation system may also include heat exchanger conduits fluidly coupled at one or both ends with the fluid conduits and extending through one or more of the gearboxes, such that irrigation fluid flowing through the heat exchanger conduit from the fluid conduits cools the temperature of the lubricant therein, thus cooling components of the drive system. The irrigation system may also include thermostat-controlled valves for allowing water into the heat exchanger conduits once a threshold temperature is reached.
