In recent years, summers in the Northeast, as well as in many other regions of the United States, have reached record high temperatures. These unusually high ambient temperatures have led to the overloading of power transformer coolers, resulting in the inability of the coolers to maintain the top oil temperature of the transformer at an acceptable level. A field-tested solution to this problem is the application of water spray onto the tube bundles of the cooler to enhance the heat transfer.Currently, the standard way of applying water to an overheated transformer cooler is to hose it down. This method has always been implemented without consideration of the spray pattern or quantity of water used, usually resulting in a wastefully high rate of water consumption.An experiment has been setup to determine the performance of a transformer cooler subjected to water spray. This work consisted of the design and implementation of a water spray system to an existing fullscale cooling loop representative of those found on actual transformers. Predictions were also made for the top oil temperature subjected to dry-air cooling and compared with experimental data. The reliability of this model shows that it can be extended for water spray applications. Heat transfer data were obtained for a range of air velocities and water flow rates on this loop. The experimental results show a significant decrease in the top oil temperature of the cooler when water spray is applied to the cooler tubes. However, the enhancement was not as significant for water how rates above 4 GPM. Distribution of the water spray through the tube bundle were qualitatively made by visual observation.