"jamesgangnc" wrote:
I think you
are confused about how inboard engine boat cooling systems work.

No, I'm not confused. I've owned and maintained a number of inboards.
Moreso than I/Os. Both gasoline and diesel. I'm apparently just not
communicating my thoughts very well.

All of them have a pump that supplies water from the outside.

And you can maintain them without hauling the boat in half the time
and half the effort of an I/O.

On the rest it's
usually mounted on the front lower side of the engine.

Good idea. No impeller in the leg at all? All of mine had an impeller
in the lower outdrive except one with it on the top.

As to the reason, it let them
build a boat with some of the advantages of an outboards but without the
finicky, easily damaged, aluminum 2 stroke engines.

And with a lot more power to push much larger boats. Outboards didn't
have nearly the HP back then as they have now. I think the basic idea
for the I/O was valid and sound. I just don't think the designers put
enough thought outside their box. They could have built a much less
complex and more maintenace free system. One with something more than
rubber boots between it and sinking. But they didn't and the market
responded by demanding huge outboards. Which it now has.
I'm not saying I/Os are a bad idea. I'm saying they could have been
less complex which usually means better.

Rick