The official Mercruiser closed cooling kit requires it. It is in the manual.You probably have an aftermarket kit.Of course, there is nothing that can stop you not to install additional pickup.

I do not get that, I have friends with both factory Merc closed cooled 525's, 600SCI and they all used the factory water pickup through the drive. Pretty sure the 39 Velocity with 565's also did.

Edit:
I just cruised through Mercurys parts catalog and can not find that part number, care to share a link to this information?

I will try creating a snapshot of the manual pages and post here, for now the entire manual cannot be upload because it is too big

If you go through this catalog, it is Y-shaped fitting, part #2, that connects to alternative transom/hull water pickup.
http://www.boats.net/catalog/mercrui...g-system-bravo

and moreover, Mercrusier's official closed-cooling kit (part 864920A02) requires an ECM change. Fortunately this one is a free swap, you buy a new one (part 866125T06) and return your original one for refund.

What are you doing with the water that use to come thru the drive?

Interesting.

maybe because it’s a full system and they feel they need more flow to cool exhaust?

I stand by my comment - I’d install without initially and monitor your temps. They move a LOT of water and I’ll bet you won’t have any issues.

Thank you for the link.

Like seaford said that is a full system including the exhaust (nice) when most performance installs do not cool the headers with the closed cooling.

I would try it without if you are using it on something like a 300hp 5.7 and monitor.
Unless the motor is out already.

Running a full system off the Bravo raw water feed depends on a few factors. Boating location and expected raw water temps. Exh manifold size and style. Fresh water circulation flow through the heat exchanger.

Generally, fresh water heat exchanged engines run a bit warmer at a 160°F thermostat, where the temp differential in the heat exchanger is greater. Also having a consistent block coolant pressure etc.

Often the full systems have the thermostat in the heat exchanger, to enable coolant flow through the exh manifolds before thermostat opening. Will also warm up the engine faster.

One of the potential coolant flow bottlenecks is the exh manifolds.

You can use it for the drive shower if you wish. I cut my tube from the upper to the helmet and just let the water dump