I don't think so. If you can duct some air from the 5.25" HDD cooler to the top most 3.5" drive, it just might do the trick. If this is a 10,000 rpm SCSI HDD in the 3.5" "rack," I think a cooler of its own would be much better. If it's a 7200 rpm IDE HDD, an 80mm fan blasting it from a short distance might be sufficient.