[C38] Overheating issue

[Michael de lisle]

So I am completely stumped and need your input.

This all started when my boat overheated and boiled off all the water in
the manifold filling the cabin with white smoke (steam). We got her back to
the dock under sail and my initial thought was a plugged heat exchanger. On
the trip back I had pulled the thermostat to check it and gave it the boil
test where everything worked as it should. As a precaution I left the
thermostat out to let the engine run cool but it was still getting hot.

 When we got back to the dock and with the fresh water circuit still in
tack I opened the bleed off valves and noticed that the fresh water I had
added to the manifold was not mixing with the coolant at the bottom bleed
off valve.

When I got down inside I found the valves for the hot water tank strapped
to the heat exchanger (HX) and the bracket that supports the HX snapped off
at the bolts and the whole mess sitting atop the transmission housing.

I pulled all the hoses and the HX plus hot water tank plumbing out and
found that the HX was actually looking pretty good. I flushed the engine
with the hoses removed and it was flowing through all the ports with out a
problem. I soaked the HX overnight anyways in a mix of muriatic acid and
water since I had it out and have yet to reinstall.

When explaining all of this to my local mechanic he suggested that the
likely problem was the fresh water pump mounted on the front of the engine.
Tonight I pulled the the fresh water pump from the block and found
absolutely no issues with it. No wobbles, no wear, no goop or corrosion.

So whats the problem???

Tomorrow I am taking the HX and the pump to the shop to have them
inspected. I am also going to double check the block with a hose to make
sure all the ports are open and free flowing. Once I get a new bracket
fabricated I am reinstalling everything with new hoses.

Has anyone got any advice as  where else I should maybe check before
putting everything back together?

I have not ruled out an air lock from low coolant in the system but won't
know if that was the issue until reinstalling everything.
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