Just guessing but since it's an I/O you probably have a heat exchanger and
therefore an outdrive impeller to provide the cool water ... and that water
may even be cooling say the exhaust manifold?

"Messing In Boats" wrote in message
...
I have a 5.7 Mercruiser and recently found that I have pumps in the
lower leg and one at the rear of the engine. It's got freshwater cooling
and even though the one in the outdrive doesn't do anything, it has to
get water to it while the boat is running out of the water or it heats
up and bends a plate and ruins the seals in the outdrive. So when I have
the boat up and warm up the oil to change it, I have a hose going to the
sea water pump and the muffs going to the outdrive. Weird.