Corroded seat for freeze cap, what to do about the cause?

[SvenH]

My boat splashed this morning.
After starting the engine I opened the water inlet (sea water cooled) and almost immediately water came flooding out of the engine.

After some inspection I found a freeze cap had released.
The cap itself is clean except for some residue which I think is some kind of hard sealant.

But where the cap meets the block is very corroded, where I expected it more or less to be bare metal if the cap had been seated correctly.



Now a suggestion by a fellow sailor has me worried.
He mentioned a saildrive as a source for corrosion, which the boat has.

But more worryingly, I've had some welding done on the saildrive before the start of the previous season and after putting the boat on the hard I found more than expected corrosion on the sail drive, which I had repainted in 2 pac paint after welding.

( the welding was because of very old damage I discovered after buying in 2007)

The boat is sea water cooled and did not visit salt water since the welding.
Inner engine anode has not been checked yet but was fine at the start of last season.

Do any of you have experience you can share?

 

[rotrax]

What we call a core plug. Although they can pop if the engine freezes, that is not their function. When a block is cast the holes into which the metal is pored need to be sealed. These 'core holes' are machined and a slightly domed plug with sometimes a tapered edge is placed in the hole and hit in the centre with a punch. This distorts it by flattening the dome, making it a tight fit.

Dig the old one out, get a new one the correct size, clean the core hole and core plug seating area, paint a bit of a good jointing compound onto the seating area and the edge of the new plug. position in the hole, dome outwards, hit it in the middle to set it.

The corrosion is another issue.

Good Luck

 

[SvenH]

Well, the core plug was easy.
The seat turned out to be in way better shape than I could recognize in my slightly overwhelmed state.
It is watertight again with the motor running well.

However, there still was a water leak and I found a crack in the thermostat housing...
Theory now is that last winter both the housing got hit with a freeze (really cold weather after forgetting to remove water from the engine) and this winter, in the absense of water started corroding, pushing out the core plug and opening the crack in the thermostat housing.

Now to find a replacement.

 

[gordmac]

Get the crack welded? Can you run anti freeze (with corrosion inhibitors) through the cooling system and leave it there when ashore for winter?