Mercury - Water Pump Repair Kit Cooling System Rebuild Multi-Piece OEM Kit 89984Q5. Overview. Anyone who's run an older Mercury or Mariner outboard - or one of the classic MerCruiser drives - knows how important a strong cooling system really is. These engines work through decades of tides, heat cycles, and long days on the water, and the hidden wear inside the water pump slowly adds up. When the telltale starts to weaken or the engine runs a bit warmer than you remember, that's your cue. The Qu