Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 224Get this manual
3 Remove the impeller, impeller key, the face plate and gaskets, (discard the gaskets)Inspect for proper bonding between the hub and the impellerReplace the impeller if improper bonding is found
a Impeller Impeller Key Water Pump Face Plate and Gaskets (One on each side of the face plate)
a Impeller Hub