"The economy figure of an engi
"The economy figure of an engine is measured in grams per kilowatt (or horsepower) and hour, but that would not tell you much, as this figure is virtually idential in all 4-stroke engines. The figure you are concerned about is fuel consumption per nautical mile, and that varies depending of the boat you have and how you run it.
If I was going to buy a used AQ120 engine (which is a B21 Volvo block) that has been running in salt water, they key things I would look for include the exhaust ports not being corroded in the cylinder head (especially ports 3 and 4), that the timing gears (sprockets) are not pitted; that the oil pan is not corroded; that the exhaust manifold is not choked or internally corroded; that all three pulleys are in good condition (not corroded); and of course, that the engine has good compression, good oil pressure and runs and idles well."