If I had this to do again, I'd disassemble the manifolds, clean them up, paint them, etc. (It was easier to do than expected, even with them bolted to the block.) But then I may have made the same error -- made by the PO -- that caused the problem we've experienced, i.e., the engine running cold.

Let's call this sketch a "schematic of concept." When the boat is started, the thermostat is closed, forcing much of the water out the Pressure Release Valve (PRV) and back into the lake. Meanwhile water in the block is circulated by the engine's pump through the engine and the exhaust manifold, picking up heat. This causes the thermostat to open and control the temperature in the engine's cooling water.

Click above for larger image.

But this is what has been happening in MacSkier:

Click above for larger image.

Why?
The photos show 1) the face configuration of both the exhaust manifolds' aft castings, and 2) the gasket configuration we found on both aft castings. The vertical slots permit the "warmed" water to mix with and exit the engine's exhaust.

XXX
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We've made new gaskets:

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Now I wonder if the "160" 'stat might have to be replaced with a "140."

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