Water Pump Impeller Kit – Fits Yamaha 15/20 HP 4-Stroke (Replaces 6AH-W0078-00-00) UanofCn You should replace them when

You should replace them when they are 50% corroded or consumed

The primary fitment requirement is the fuel line's inner diameter

or brittleness in the rubber

or trailering

Water Pump Impeller Kit – Fits Yamaha 15/20 HP 4-Stroke (Replaces 6AH-W0078-00-00) UanofCn You should replace them whenProduct Details This Water Pump Impeller Kit provides all necessary components for a complete service on select Yamaha 15 HP and 20 HP 4 stroke outboard motors manufactured from 2006 onwards. It is engineered to restore the cooling system's performance and reliability, preventing engine damage from overheating. This kit is a direct aftermarket replacement for Yamaha part numbers 6AH W0078 00 00, 6AH W0078 01 00, 6AH W0078 02 00, 68T W0078 00 00, and