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Old 05-08-2009, 08:44   #1
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Freshwater-Cooled Diesel - A Stupid Question

reviewing a spec sheet for a boat, noticed the inboard diesel was listed as fresh water cooled.

does that mean engine won't function properly in salt water?

If yes, is there a simple inexpensive retrofit for salt water cooling?

thanks for your advice
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Old 05-08-2009, 08:49   #2
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It means the cooling of the engine is self contained. The water pump">raw water pump, sea water, cools the engine's water with an outside source via the manifold.....i2f
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Old 05-08-2009, 10:15   #3
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Just to expand a bit on i2f's explanation. Fresh water cools the engine, just like a motor car. Instead though of a fan sucking air through the radiator to keep the fresh water cool, a marine diesel sucks up sea water to cool the fresh. This sea water is what you see coming out of the exhaust pipe when the engine is running. It is therefore important to check that you do indeed have waqter coming out with your exhaust, otherwise it tells you that no sea water is flowing (and therefore cooling) your freshwater (which of course in turn is cooling the engine!)

Just 2 threads below this one, read "Engine Overheats, Raw Water Problems - help". Raw water is actually the sea water. Tony
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Old 05-08-2009, 13:22   #4
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Old 05-08-2009, 13:50   #5
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Only stupid answers.

I don't mean the ones on Cruisers' Forum of course.

George
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Old 05-08-2009, 14:29   #6
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The alternative is a 'saltwater' cooled engine, be it fresh or salt. What these cooling systems do is pump the water that the boat sits in through the engine for cooling. The disadvantage is that in salt water you have the all the stuff in saltwater being circulated through your engine. The advantage is that they are simple, no radiator, less weight and need for room to house the radiator system.
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Old 05-08-2009, 16:50   #7
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If you've got one of those - keep your eyes on the zincs....they can go extremely fast and are the only thing protecting you from engine melt-down! Tony
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Old 05-08-2009, 17:59   #8
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What needs to be mentioned is that the device used to remove heat from the fresh water (water and ethylene glycol actually) side of the cooling system to the salt water side of the cooling system in a typical marine Diesel engine is called a heat exchanger.

A marine diesel heat exchanger might look like this.


...and works like this.

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Old 06-08-2009, 08:19   #9
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thank you gentlemen,

that was all quite helpful.

FM
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Old 06-08-2009, 15:13   #10
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Aloha First Mate,
Just to add to what others have said. If you see a listing for a freshwater cooled diesel engine on a boat it is preferrable to a saltwater or rawwater cooled because it keeps the saltwater out of the waterjackets of the engine where it can corrode away from the inside.
So a freshwater cooled engine is on the plus side. Well cared for diesel freshwater cooled engines may be still be running after 5000+ hours.
Kind regards,
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Old 06-08-2009, 19:31   #11
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Just make sure you religiously change the zoncs in them...they are usually small.
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