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Discussion Starter #1
Anybody here use a closed cooling system in their jet boat.

The reason I ask is were building a new motor to run circles and the builder would like to control temps better.
 

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Ron I've sold "closed" systems to guys that run in salt and brakish water , they rquire a lot of rigging but work similar to a automoblie system , They require a (raw water cooled) heat exchanger, cirulating pump etc . Gotta ask the "gain" is worth the complications and extra rigging and weight Tom
 

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Used a San Juan heat exchanger on the River boats, it does require a waterpump on the engine (really not a big deal), the funny part is you can actually gain more HP than you lose to turn the water pump and belts, The weight gain is about 40# (+/-).

I don't know if you would benefit from the closed cooling (we used to run our junk in a Pacific Ocean Harbor), but can get some awsome control of the temps with just a circulating pump. Have you ever considered running the cooling system backwards?

You can put the inlet water through the bottom of the block and control the outlet in the heads via an inline thermostat, the beauty is you can get two outlets on each head allowing better temps throughout the engine as an assembly without anything else to break..Just an outloud thought...

GT :)hand
 

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I've considered this, but I didn't see any way to maintain the water exit temps my engine/tune requires(125-140 degrees)

Would love to run in the Pacific but I dont want to sacrifice my aluminum heads to the saltwater.
 

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So if looks arent an issue we just run a alumi radiator with a mezieres electric water pump and a thermo just like a car. The radiator doesnt have to be that big because it will be out in open air and the motor will only be running for 15 minutes. This means lets find a 19 flat deck with center steer and cav plates;). I still don't know enough about the heat exchanger to like it. I know conventional cooling system though.

Or the cheap way to do it is run a restriction in the outlet of the engine. You already have the pressure relief on the pump. A 5/16 hole on the outlet should be pretty close to 200 degrees at 15 psi block pressure. Just figure out a quick way to switch the restriction and go play with it till you find the right combo. Its not a closed system but will get the same results. minus the crap in the water passages.
 

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Discussion Starter #6
Thanks Tom and Glen, I had looked at Mercury Marines site but didn't see anything about the capacity of these systems.
I was thinking heat exchanger, thermostat and an electric water pump, is that about it?
Motor will be a 502 around 13-1 cr and be running 6000 - 6500 for 10 minutes at a time. Do we just run the same 1/2" line from the pump through the heat exchanger, and how big of an exchanger do we need.
Glen you lost me on the advantages of the backwards thing.
Part of the reason he wants a closed system is so he can build the motor tighter. With the open systems the block doesn't expand like the pistons and he has to build it looser than he would like. Also with everything new on this build i'm sure he doesn't want hard water combined with sand and debris in his motor.
Do you guys have any pics of these systems?
 
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