Sounds like you have a few issues going on. The head gasket probably needs replacing and resurfacing or replacing the head will help it seal better. If you do it check and clean out your exhaust manifold really good and check and or replace your riser. Seen a lot of good running motors ruined by overheating and bad rotten risers and clogged manifolds.
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77 V20 cuddy with 170 I/O Mercruiser
72 16ft. Carolina w/a 25hp Evinrude
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