4BY150

The 4BY150 is one of the four engines of Yanmar's original BY series (4BY150, 4BY180, 6BY220, 6BY260), introduced in 2006. The BY engines were developed with BMW on BMW diesel blocks - 1.995-litre four-cylinder and 2.993-litre six-cylinder, 84 x 90 mm, double overhead camshafts, four valves per cylinder - marinised and assembled for Yanmar in Europe - with electronically controlled common-rail injection and a CAN bus on the NMEA 2000 protocol. All four are rated at 4000 rpm.

Inboard versions were shown with the Kanzaki KMH40A gearbox. The sterndrive versions carried a Z suffix (e.g. 4BY150Z) and were matched to MerCruiser Bravo X-1, X-2 and X-3 legs; Yanmar's own ZT350 sterndrive arrived only with the second generation.

The BY series was replaced at the end of 2008 by the BY2 series with the same ratings, then by the BY3 around 2013, and the whole family was eventually superseded by the 4LV series from 2017. Used-boat listings often write these engines without the generation digit, so a '4BY 150' or '6BY 260' can be any generation.