This article presented experimentally a study on the flat fan nozzle and the impact of the nozzle's input parameters on its performance with oil as a high viscosity coolant, as well as estimating their performance, spray characteristic, and heat transfer coefficient (HTC) during the design period. For this purpose, the test bench was developed, and NF0390, as a commercial flat fan nozzle with a medium spray angle, was selected. A series of experiments are carried out, and the impact of various nozzle input parameters is investigated. The nozzle's performance is investigated by heat transfer capability, temperature rise and providing temperature uniformity. Several suggestions and tips for more efficient and even temperature and cooling performances are proposed. © 2024 IEEE.