Coolant diverters in a boat?

My question is if you have a marine water pump do you need the diverters? I have block off plates were the OE water pump bolts up to the block. There are no diverters currently in the boat and i have to assume the previous owner operated the boat like that. The impeller is external driven off the cam and directly flows water into the bottom of the block after it flows through the exhaust log and comes out the top of the intake and then into the riser and out the exhaust.

You threw me a little with the term diverter as in a divider. But I now get your question.....

What you have is another way of cooling the motor from a different water flow path, from the bottom up. Depending on where the water is entering the block, the size of the ports or fitting leading into the block or only one side vs. feeding the block from both drains, this way has been done for many years by some boat guys. The idea was to cool the rear or the furthermost part of the block/heads away from the water pump. If done right it works great. If this is new to you, I'd check with a temp gun to make sure things are cooling properly just to CYA.


The water should be preheated before it hits the block to build some heat into the motor, as you drive on your radiator in a boat! The water never gets hot in the radiator! So throwing a little heat in goes a long ways in a marine motor.


In my Dragboat with headers it's, lake, pump, block (at OEM water pump ports), and out the intake, then overboard. I control my heat when needed by restricting the outlet flow. Never restrict inlet flow with a rubber impeller pump as you will likely induce "pump cavitation" and lose your ability to cool the engine.

Either cooling method will work as they both have been proven over the years.....just make sure yours is up to snuff.

Hope this helps......