145 posts
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?
NSW
7757 posts
Bit of a tough one and probably not something that's worth worrying about. Are you on a swing mooring or marina? have shore power? Anodes on the hull connected by earth rods to the machinery and engine block? Prop shaft connected electrically to the engine block, do you have a plastic drive shaft adapter fitted? Any "rust" streaks down the side of the hull from fastenings, how damp is the timber? Stray currents or false currents in the timber?
These are the sort of stuff wooden boats have. My old fishing boat was 68 years old when I sold it. It had a Gardner main engine and had few gaskets and controlled corrosion by leaking oil everywhere. Try spraying or smearing Lanolin over your engine.
