I'm assuming its a transmission cooler. The internal rad mounted cooler is less than optimal as it can only "cool" the ATF to 195 degrees. The shop that rebuilt my transmission, installed an auxiliary cooler. It was mounted to the radiator with some kind of straps that wrapped around the cores. I didn't like that, someone who off-roads once told me this system caused a catastrophic radiator failure. So, I fashioned some stainless brackets that are attached to the rad support, keeping the cooler separate from the rad. Also, wherever the hoses come into contact with metal, I cut another larger diameter hose and slipped it on, with zap straps to hold it in place. This prevents any chaffing, and potential hose failure in the future, from all the vibration.