Mercury - Water Pump Kit Cooling System 46-42579A07. Overview. This kit restores the heart of the cooling system-something you really notice after a few seasons of sand, silt, and shallow-water runs. When the impeller starts wearing down, the engine can run hotter than it should, especially during long idle periods or slow trolling. Swapping the whole kit gives the motor a fresh, steady flow of water again. It's a job most boaters take on themselves, and this kit has what you need to get the pum