Could be a B20.

5 years ago I spent a couple weeks in Sweden on a consulting job about 1 hour west of Stockholm. One evening walking by the lake shore I saw a bulletin board with lots of notices of boats for sale. Of course most of the wording was in Swedish which did not help. But from what I could make out, I saw that a lot of the small boats had B18 and B20 engines. Them smart Swedes know a good engine when they see one!

Typically, true marine engines are more like truck engines than car engines since they need to be built tighter and tougher. After all, boat engines spend more time under heavy loads plowing through the water. Car engines can be built looser since they only see heavy loads when the gas is really womped. I remember reading someplace the B18 was based on a 3.6 liter V8 truck engine. Volvo essentially sliced off one bank of cylinders and turned it into a 4 cylinder engine. The crank bearing was then changed to accomodate the new configuration. Hence, the B18 and B20 engines have the heart of a truck engine which makes them near bomb proof. No wonder they make good boat engines.

In general, Volvo makes a good marine engine. The Volvo Penta outdrives I hear are very good. Expensive, but what else is new from Volvo. My father has a 3 cylinder Volvo diesel marine engine in his 30' sail boat. Engine was designed from the ground up as a marine engine. He says that engine is probably the most reliable thing on the boat. Every spring he turns the key, and the engine fires right up after winter storage. When cruising under power, he burns 1/3 gal per hour. Not bad!