Join Date: Apr 2006
Location: SE Alaska
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This is an interesting discussion. I don't have a Yanmar. My Volvo tranny drinks the 15W-40 stuff, same as the engine, nice and convenient that way. Never heard of ATF on a boat, but it makes sense in a lot of ways. Many newer gear boxes, transfer cases & such use ATF. It is better for fuel economy, and probably better at resisting emulsification than heavier oils.
I think ATF is chemically similar enough to motor oil where it won't damage the seals, might actually help a little. However I agree that it would be prudent to have them put in the correct oil based on the published tranny specifications.