Yanmar SD20 Saildrive in TechTalk Posted September 20, 2020 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.