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Yanmar SD20 Saildrive


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Changed boat last year and for the first time now have one with a saildrive. I'm very pleased with the performance - no issues and no propwalk. However, and maybe I'm missing something obvious here, I have a concern about the oil. When the drive heats up with use, the oil obviously expands. There is no breather, so where does it go? Would it not be pushing out through the bottom seals? And, conversely, when it cools down, would that not promote suction of water back through the seals.? I looked up the coefficient of expansion of lubricating oils, and it suggested that for a 25 degree rise in temperature, the expansion would be about 2%.

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SD40's have an oil expansion issue. A good fix is a brass fitting tapped onto the top fill plug, with a hose to a bottle.

Oil if pushed out just flows in & back out of the bottle.

Yanmar, love the engines, hate the saildrives. But the 20 is the best of them, very few issues with them, unlike the clutch/cone problems with their bigger brothers.   

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Ah, you would think so. But, on this boat, the water intake for the engine has been set up to come from a seacock in the boat directly into the 3GM. That would mean that the cooling water for the saildrive is not circulating through the drive, just passive cooling in the water. I wonder if that is an unusual set up. I have heard that it's a common problem that the saildrive intake holes are fairly small, and often get clogged with barnacles etc, so this setup might have been a way to avoid that. However, I would have thought that 25 degrees is not actually huge, we are talking about 15 degrees to 40.

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moving the cooling off the sail drive is fairly common as the holes block up and the on/off valve often seizes,  i have only ever had sail drive and all mine have been like that no issue.  New had an oil expansion issue,  just make sure that the level is correct and it works itself out.  Also check oil is not milky as that indicates water getting in the bottom seal.  When antifouling crack the drain plug and make sure the first drops out are clean.  If you need to to the bottom seal it is a simple DIY job when on the hard. 

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