1 have merc carb 2006 overheats against hard tide or in canal temp stays in middle when up on plane water pump and thermostats are not that old seems to be enough water output ?
What's WOT rpm. If it's a little on the low side, you might be overloading it a bit when yer in mush mode. At the same time water delivery is lower. One or two degrees too much spark advance could do it, also. If yer running 87 octane, try 91 non oxygenated for a bit and see what happens.
