Mercury - Water Pump Assembly Alpha Sterndrive Cooling System OEM Composite & Metal 8M0113733. Overview. There's a certain comfort that comes from knowing your engine's cooling system is doing its job. When you ease the throttle forward and feel the boat lift, that quiet confidence is built on the small parts you rarely see - like the water pump keeping everything cool and steady beneath the deck. The Mercury 8M0113733 Water Pump Assembly delivers that kind of trust. It's the part that lets you