Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 350Get this manual
3Remove the impeller, impeller key, the face plate and gaskets, (discard the gaskets) 3Inspect for proper bonding between the hub and the impellerReplace the impeller if improper bonding is found
70605ImpellerImpeller KeyWater Pump Face Plate and Gaskets (One on each side of the face plate)
aImpellerHub
4Inspect the impeller blades to see if they are cracked, burnt, hard or deformedReplace the impeller if the blades are in this conditionIMPORTANT: The circular groove formed by the impeller sealing bead should be disregarded when inspecting cover and plateThe depth of the groove will not affect water pump output
WATER PUMP ASSEMBLYComponent Inspection
1Inspect the water tube coupling assembly for wear or damageIf necessary replace the worn or damaged components especially the two 0rings on the inside, one at the top and one at the bottom