For decades there was always a regular water circulation pump mounted on V8s for inboard and I/O applications. Then Mercruiser did some without the circulation pump, only the raw water pump. Which brings up the question, is the raw water pump really all that's needed? I just want to be sure before I delete it on my 565cui build.
Thanks

I'm so glad you started this thread. I Have been wondering the same thing. Looking forward to the educated responses.

I swapped mine out for a stainless marine crossover years ago. Never experienced any issues.

I've been on both sides of this over the years. The cost to remove the water pump compared to what you get in benefit from it. Pulling that center pully out of the mix can be a big pain in the ass when it comes to getting everything else to work. Then there is the loss of the circulation pump. Maybe not an issue with the hammer down but if you get caught in a few 6mph zones you can get hot spots. It was explained to me the same way as when not running a thermostat, without the resistance of the closed thermostat the cold water will flow through the block like a river leaving the hot water on the riverbanks (hot spots). Then there is the issue if you can run a thermostat or not. A lot of them dont allow it so either you dont use one or you have to come up with some sort of bypass like the old Chrysler inboards used and they still kept the circulation pump because with a bypass the water is no longer "forced through" the motor. No thermostats even in my state of Maryland means cold motors. Then of course you have to make sure your raw water pump is up to not only presenting cold water to the circulation pump but also able to push it through the motor and out the exhaust on its own. And it just goes on and on from there.
I have a bypass(s) sitting on a self out in the garage now and I've thought about putting on my drag boat or my offshore race boat with Kiekhaefer race motors but my drag boat is from 1959 (Beiesemeyer) and the offshore race boat is from 1968 (Nova 24). They spend more time in 6mph zones and putting around in marinas and the local beach hangout then they do racing (I dont race them, just blast on occasion). The circulation pumps are on all of them still.

Lot of reports of high water pressure when running with crossovers, make sure you have a relief if you are running one!

I thought on big HP the more water the better for cooling. Cooler heads= less chance of detonation
But then there are guys who say you want heat in the engine and it`s more "thermally stable" with a water pump.
I dont know .
Seems most builders that do big power don`t have water pumps but any Mercury engine that is closed cooled has one so .. ****ed if I know

Don't think it matters much up and running (assuming water press is OK), however I could imagine steam pockets (hot spots) forming when dropping into a no wake zone after a hard run w/o a circulation pump. Maybe more so in a small boat since they have to idle down more than others to prevent a wake?

Closed cooling has to have a circulation pump. Same set up as a car only its water to water. Being freshwater cooled and how stable it would be was kind of what I was wondering about. I was thinking, maybe wrongly so, that a restrictor would stabilize it some. On hi perf auto applications a gutted thermostat does a very good job and restricting enough water that it stays cool while running hard, yet doesn't overheat when idling. Wonder how that'd work with a pressure dump like on jet boats to keep from building excess pressure?