Re: Mercruiser 3.0
I second that. I had a 19 footer with a Merc 3.0 in it and got just a shade better than 40 mph out of it. Very good for skiiing, tubing or just cruising around.
And, now that I've upgraded to a V8, I can see a difference in gas mileage...
While others with more technical knowledge will likely chime in, Merc has been making that motor for years - so that should tell you something.
I also second the notion of getting it looked at. There are plenty of Merc mechanics out there that have seen a 3.0 inside and out and can tell you if it's worth it to spend the money.
Good luck...