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Old 01-27-2016, 08:56 PM   #1
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Default closed cooling question

1998 2800 scr carbed 7.4 mercruiser

3rd season with this boat (fresh water lake) and we are going to have it a very long time.
I was reading that a closed cooling system is better for the engine and longevity. I'm guessing that the impeller moves lake water acrossed the heat exchanger for cooling right?
Curious thoughts from those here or input from anyone who has done the conversion. Is this worth doing and really help the engine last longer?
thanks
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Old 01-27-2016, 10:29 PM   #2
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If you boat 100% of the time in fresh water than going to closed cooling will have little impact on the engines longevity. Salt corresion is what shortens water jacket life. IMO if properly maintained a raw water cooled salt engine will last nearly as long as a fresh water one and both will die from normal engine wear. The difference is the fresh water one can be rebuilt while the salt on will have too much corresion to make it worth while.

Yes in a closed cooling system the raw water pump provides sea water to the heat exchanges to transfer and carry away the heat. Note there are partial and full systems, the partial only provides closed cooling to the engine and the full includes the exhaust manifolds.

Closed cooling means you only have to winterize the open portion of the system and flush the closed side as recommended but about every 5 years.
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Old 01-27-2016, 11:25 PM   #3
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AND..... Closed cooling lets the engine operate at or closer too the temps it was designed for, thereby burning fuel more efficiently. Also, all the internals of the engine will see glycol which has rust inhibitors, as well as lubricates for the circ pump etc. IT ALSO keeps sand, shells, and other CRAPOLA out of the engine/manifolds, if full cooled.
It's also adds resale value!
I'm a HUGE believer in closed cooling, if you couldn't tell!
I buy and sell many, many boat, and I always convert over. Who wants to deal with winterizing and possibly having thousands of dollars of damage, just because you misjudged! Not to mention, just a pain in the arse!
If you leave out of the water, or in a no heat situation, you'll need to drain the coller, but no biggie.
One of the things, I like, is we can go down to the docks, fire up the twins and take off, whatever the outside temp!
But that's just me!
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Old 01-28-2016, 02:33 AM   #4
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Not sure I agree it adds to the resale value in dollars but helps as a resale perk.

Yes it can keep crud out of the engine but it will still end up in the HE.

I do like closed cooling for corresion and less concern on what needs to be winterized, most espensive part (engine) is protected in case you wait too long or screw up.
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Old 01-28-2016, 04:37 PM   #5
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Everything that sees salt water is flushed with freshwater. I run my drive on muffs and hook it up to a small pump in a bucket of propylene glycol. I have to sit there pouring more Ant-freeze into the bucket as the pump and engine runs. Once done, I also don't worry about what was winterized and what wasn't.

I do have closed cooling, but the 8.1 was designed weird. The fuel pump cooler is lower than the water pump drain so it doesn't get drained properly. This is easier than disasembly.
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