Mercury - Quicksilver Water Pump Impeller Cooling System Component Marine-Grade Elastomer 42038Q02. Overview. A dependable impeller is the heart of your outboard's cooling system. The Mercury Marine 42038Q02 Quicksilver Water Pump Impeller delivers the water flow your engine depends on to stay cool and run efficiently. Designed for Mercury and Mariner 6-15HP TwoStroke outboards and select 8-15HP FourStroke models, this OEM impeller uses flexible, marine-grade rubber that holds its shape under pr