[Sans Peur]

I have owned a few gas inboard Mercs and all of them had heat exchangers and coolant running in the engine. None of them had coolant running through the exhaust manifold and elbow. The exhaust manifold and elbow always had raw water running through them.

Raw water came in from the impeller pump,through an oil cooler, to the heat exchanger and then to the exhaust manifolds and finally up into the elbows (shower heads) and out the side of the boat with the exhaust. Manifolds get clogged internally and will overheat. They are a "wearable " item and have to be replaced periodically.