Mercury - Water Pump Repair Kit Outboards & Alpha Sterndrives Complete Cooling System Service 89984T5. Overview. Cooling system performance is everything when it comes to engine life. Even a slightly worn impeller or damaged gasket can reduce water flow and cause the engine to run hotter than it should. The Mercury 89984T5 Water Pump Repair Kit restores factory-spec cooling performance by replacing the essential components that wear out due to sand, silt, debris, and normal use. Designed for a w