According to US Coast Guard regulations
Is this thermostat for raw water or freshwater cooling systems
Place a new gasket (sold separately) on the housing and reinstall the cover
and check for any exhaust or water leaks
Position the sterndrive in the trailering position and properly support its weight
Water Pump Impeller Kit – Fits Mercury Marine 25-50 HP, Force 40-50 HP (Replaces 821354A2, 821354A1, 821354A04, 18-4531) 5.5HP According to US Coast GuardProduct Details This Water Pump Impeller Kit Fits Mercury Marine 25 50 HP (Replaces 821354A2, 821354A1) provides all the necessary components for a complete water pump overhaul. It is designed for Mercury Marine 25 50 HP 4 Stroke outboards from 1998 and newer, including 25, 30, 40, 45, and 50 HP models. It also fits select Force 40 50 HP engines from 19951997. This kit serves as a direct replacement for Mercury Quicksilver part numbers 821354A1,