Mercury - Impeller Cooling System Component Marine Elastomer 8M0200115. Overview. Every boater knows that a smooth-running engine isn't just about horsepower or throttle response. It's about trust - trust that your cooling system is pulling water the instant your engine turns over, trust that the temperature stays steady even when the sun is beating down and the boat is loaded with gear. The Mercury Impeller, part number 8M0200115, is one of those unsung components that keeps everything running