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post #1 of 2 Old 05-30-2012 Thread Starter
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yanmar engine gasket corrosion

I have a sea water cooled Yanmar 3GM30, installed as new 3 years ago in a wooden yacht and only 120 hrs engine run time. I replaced 2 of the 3 anodes 7 months ago (I've only just discovered the third anode hidden behind the fuel filter). The previous anodes were about half corroded.
A few months ago I noticed some white powdery substance around the plastic screw that drains the engine block near the fuel pump and a little around the head gasket. I wiped it off and recently checked it again. It is worse and appears on about 4 inches on one side of the head gasket near the fuel pump, about 3 inches on the opposite side of the head gasket, around the engine block drain plug again and also around about 1 inch of the water pump gasket. I'm concerned that the corrosion may be inside the engine and not just the outside where the gasket (presumably a copper alloy of some sort) meets moist air. I'm guessing the problem is galvanic corrosion from contact with sea water in the engine block but I thought the anodes were supposed to stop that.
The negative from the battery to the engine block is always connected but the positive from the battery to the starter motor is always isolated when not in use.
Has anyone seen a similar problem and found a solution?
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post #2 of 2 Old 05-30-2012
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Re: yanmar engine gasket corrosion

I am not quite sure what the problem might be. I have a sea water cooled Yanmar 3gmd that is 30 years old and do not see this problem. I did change my 3 engine zincs about a year ago. When I changed the zincs, there was nothing left of the one that was replaced. I imagine the engine had been used for many years with no zincs (the zinc plugs were very difficult to remove- rusted in place). The engine had been used so while I will change the zincs, I am not sure how effective they are as the engine did not seem to be corroded, but it is cheap insurance to have good zincs for whatever they are worth.

I think you may have either aluminum poultice corrosioin or maybe the white stuff is salt left when a small sea water leak evaporates of the water and salt is left.


Was the engine a rebuilt one? Looks like maybe the gaskets are leaking (salt water) due to improper torques of the bolts. I think the engine may be older than 3 years as I think Yanmar now sells only fresh water cooled engines with a salt water heat exchanger.

Looks like the engine is a minimum of 7 years old:

Last edited by casey1999; 05-30-2012 at 03:48 PM.
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