Merc Gen II water pump service.

The Mercruiser Gen II water pump should not be ignored until a overheat is experienced. Serious damage could have occurred to the engine long before the overheat warning buzzer goes off. 
The fault lies in the tendency of this pump to ingest air/ exhaust gas into the cooling system. Corrosion develops under the pump gasket and warps the water pump base plate causing the gasket to leak. The water and air mixture allows head temperature to run much higher than it should. 

   Seasonal service should prevent this from happening and the potential for engine damage. Usage in salt and/or brackish water requires special care when servicing this pump.


Note corrosion surrounding the pump housing at the base of the pump.

A closer view shows the factory paint in still on the gear housing... unfortunately...

Removing the paint shows that the corrosion is quite extensive under the paint.

Carefully remove all the dead paint.

And sand the surface clean.

Note: Pencil placed in oil passage hole to 
help keep dirt out of oil passage.

Paint the bare casting with Zinc chromate primer then with regular paint before applying gasket sealing compound. Complete the assembly of the water pump per the manual.

At the center right of the picture you will note a piece of debris is clogging the weep hole of the water pump base plate. This hole needs to be kept clear and care needs to be used when applying the gasket sealing compound so that the hole does not get clogged with sealer during assembly.

The above information should be used in addition to your service manual.

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