Mercury Optimax Models 135, 150, Direct Fuel Injection., Page 289Get this manual
COOLING
Water Pump Cleaning and Inspection
1Inspect the water tube coupling for wear or damageIf necessary replaceaWater Tube Coupling 2Inspect the water pump impeller for wear on the end, top and bottom of the impeller bladesReplace the impeller if this condition is found3Inspect for proper bonding between the hub and the impellerReplace the impeller if improper bonding is found
aHubImpeller 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 output5Replace cover if plastic is melted from excessive heat (lack of water)Replace stainless insert andor face plate if grooves (other than impeller sealing bead groove) are more than 0.010 in(0.254 mm) deep