[Fr. Frank]

The outdrive pump has nothing to do with engine cooling on a fresh water cooled closed system.

NO! NO! NO! The impeller in the outdrive is what feeds water to the heat exchanger and in most cases, (if you have one) the raw water pump. If you don't have raw water pickups on the hull bottom, you desperately need good impellers in your lower unit. BTW, the outdrive has no need of cooling, it sits in the water.

Most fresh-water cooling systems use engine coolant just like a car, and in many cases, the engine coolant also cools the exhaust manifold. The raw water is injected from the heat exchangers into the exhaust risers after the exhaust manifolds, and then through riser to outdrive hoses.

However, there are still a lot of engines where everything after the cylinder heads going outward is raw water cooled. Most Mercruisers are like this.

I had a 255 Wellcraft SunCruiser with twin V6 stringer drives, and I have had a FishNautique with a Pleasurecraft inboard, and both used exhaust manifolds that were cooled by the closed cooling system. The OMC's actually used the exhaust manifolds as heat exchangers.