4BY2-150

The 4BY2-150 belongs to the BY2 series (4BY2-150, 4BY2-180, 6BY2-220, 6BY2-260), which Yanmar announced as the successor to the original BY series, 'available end of 2008'. The outputs stayed the same - 150 and 180 mhp from the 1.995-litre four and 220 and 260 mhp from the 2.993-litre six, all at 4000 rpm - but Yanmar listed a fully water-jacketed exhaust manifold, turbocharger and heat-exchanger changes, a metal top cover, a glow-plug controller, a combined fuel manifold, a new two-piece flywheel housing and ECU software changed from torque to speed control for smoother running and better twin-engine synchronisation.

Inboard versions were listed with the Kanzaki KMH40A gearbox. The Z-suffix sterndrive versions could be ordered with Yanmar's own ZT350 sterndrive, which Yanmar developed for the BY2 and LP engines, and BoatTEST also mentions MerCruiser Bravo legs as a pairing.

The BY2 appears on Yanmar's line-up until 2012-2013, when it gave way to the BY3 series with the same ratings. BoatTEST's review of the 4BY2-180 notes its use in small trawlers, sports boats over 20 ft and petrol-to-diesel repowers.