Mercury - Water Pump Repair Kit Four-Stroke Cooling System Marine-Grade Components 8M0205803. Overview. Any boater who's spent long days offshore or lazy evenings drifting near the inlet knows how much trust we put into our engines. That steady hum, the smooth throttle response, the confidence that the temperature needle will stay right where it should - all of it depends on a healthy water pump. When that system is working right, you barely think about it. But when it falters, you feel it insta