AD31

AD31 is what Volvo Penta called the 30-series diesel when it was sold as a complete Aquamatic sterndrive package rather than a shaft inboard: the same 2.4-litre, four-cylinder, direct-injected, turbocharged and aftercooled engine as the TAMD31, mated to a Duoprop drive with counter-rotating propellers and power trim. The line ran through A, B, L and P revisions (the earliest sold as AQAD31), the L and P being the final ratings at 130 and 150 hp. It was the standard diesel for mid-size Nordic day cruisers and cabin boats through the 1990s, and it is the designation a used listing names when the boat has a diesel sterndrive of that era - which is also where the buyer's attention should go, since the drive and transom shield are usually the expensive part.