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Discussion Starter · #1 ·
We have a 3 GM 30 Yanmar in our boat. The engine looks and runs like new, but is about 10 or so years old and has been properly maintained since new.

The other day I climbed into the lazarette to check the Racor, which is behind the engine. At the rear of the engine is a 2" X 2" flat plate held on with 4 12MM bolts which also secure the engine lifting eye, and a small clamp securing a hose. On the top and bottom of the plate where the edge touches the engine, there is a white powder substance which looks like shaving foam emerging from the crack between the two surfaces. It is dry and I cannot find any trace of water leaking from the area.

This is the second time it has appeared in a month. The first time I washed the area down with distilled water and assumed that something had spilled there.

I suspect it could be corrosion as I have had experience with a similar appearing substance on aircraft. I cannot be certain but do not believe that there should be any salt water contact at that location. I am wondering if the heat exchanger has been compromised, allowing salt water into the fresh water side. Yanmar uses no anodes in this particular engine. I detect no salt contamination in the cooling water, which appears normal in color. I have no idea what is behind the plate and need to determine that before removing it.

Any ideas or suggestions?
 

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Discussion Starter · #3 ·
Great idea, will try it in the morning. There could be a gasket but if so it is not visible.

It seems that if the exchanger was compromised the water level in the reserve tank / overflow, would not be at or stay at the proper mark as salt water entry would allow fresh water exit also. Hope it is something simple as heat exchangers are costly items.
 

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Discussion Starter · #5 ·
Is there gasket behind the plate that is failing? I'd clean it off and climb down there with the engine running. bring some soapy water. put it around the plate and look for bubbles.
Thanks jsaronson, tried the bubble test which was negative.

gamayun, you are probably right, and that would be a good thing. Did not want to remove the plate until I determined what was behind it and if coolant would be at that high level with the engine off. I wanted to be prepared in advance if possible. Could find no reference to it in the service manual. Must just be corrosion, not salt, caused by dissimilar metals, as there is no good reason to have salt at that location.

Thank you both
 
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