Mercury - Water Pump Impeller 4-6 HP Four-Stroke Series Marine Elastomer Construction 8M0204676. Overview. There's a certain comfort in knowing your outboard is staying cool, no matter where the day takes you. When you're running a small four-stroke - slipping along a quiet shoreline, pushing through a narrow creek, or heading back with the sun on your shoulders - you want that steady, reliable flow of cooling water you don't have to think about. That's exactly what this Mercury Marine part deli