Technically excretion does lower the total thermal energy of the body as it is leaving your body with the excretion, but it does not really in itself cool down the temperature of the body as the temperature is the same as your body (unless you define cooling down as negative change in the thermal energy needed to remove to lower object’s temperature to zero K). Though if for example you drink cold water it does cool your body very slightly and urination could be thought of as dumping of used coolant.