Friend of mine has a 1985 Mariner 30 attached to a small fishing boat. The engine ran great up until about 2 months ago when it would slowly overheat and kill the engine after about 4 minutes of running it. Pulled the bottom of it off to find a fucked up impeller, so replaced that and took it out for a test yesterday. Ran fine for about 4 minutes then slowly stalled out, smoking a little bit. It wouldnt restart, but would crank over fine.
Now, what could possibly be causing this thing to overheat like that? He believes he didnt mix the gas right, but could that have that big of an impact?