Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 271Get 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 -
aImpellerImpeller KeyWater Pump Face Plate and Gaskets (One on each side 01 the lace plate)
Impeller
WATER PUMP ASSEMBLY COMPONENT INSPECTION 1Inspect the water tube coupling assembly for wear or damageIf necessary, replace the worn or damaged components especially the two O-rings on the inside, one at the top and one at the bottom