Yamaha Thermostat Housing Corrosion

[eelpots99]

I boat a used boat a couple of years ago with a 2003 Yamaha 225 4 stroke and just became aware of corrosion issues. I noticed today that my thermostat housing is corroded where the hose fits over the nipple and water is coming out. Do I need to do more than replace the thermostat housing and thermostat?

[boscoe99]

I would remove the housing and carefully inspect the section of the block into which the thermostat is positioned. Some blocks can have a hole eaten into them in that area. In a saltwater motor if saltwater is sprayed out of that hole it can do significant damage.