On Mon, 22 Feb 2016 19:32:24 -0800 (PST), Tim
wrote:

My manifolds are freshwater cooled. Elbows will be the only thing needing
replacing. I have closed cooling, with heat exchanger.

Closed system is actually the best way to go. a friend of mine loves to boat about year around that is when he can, and installed a heater core in the cuddy so he can duck inside and get warmed up.

Plus, the automotive style engine can warm up to a toasty 180 degrees and run more effeciantly than thee usual 130 degree raw water system.

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A fresh water boat can change out the thermostat for something hotter.
The only reason for 130 or 140 is to prevent salt from crystalizing in
the cooling system.