A working fluid cooling control system of a construction machine capable of reducing the troubles and increasing the life of hydraulic devices and preventing such problems as the increase of noise and the deterioration of fuel economy from occurring by increasing a cooling performance before the temperature of a working fluid is increased to prevent the temperature of the working fluid from being increased. A controller (100) receives signals from a traveling motor speed pickup (101), a pressure sensor (102), a signal receiving line (103a) of an optional selector switch (103), and a temperature sensor (104), performs predetermined calculation treatments, and controls proportional solenoid valves (105, 106). The controlled pressures by these solenoid valves are compared with instruction pressures positively controlled by shuttle valves (109, 110), and the higher pressures are led to tilt control mechanisms (13, 14). In an operation pattern in which the temperature of the working fluid is increased, the minimum tilt angles of hydraulic pumps (11, 12) are increased to increase the averaged flow of pressure oil passed through an oil cooler (40) to increase an averaged heat discharge amount so as to lower the balanced temperature of the working fluid.
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