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Old 13-10-2012, 20:19   #1
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Boat: Catalina 350
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Engine Cooling

Can anyone explain the pro and cons of raw water versus fresh water cooling in a Yanmar 3-cylinder diesel engine. I have been seeing boats with identical engines but cooled one way or the other. Does raw water cooling shorten engine lifespan and/or lead maintenance issues?
David in N. Florida

David Hipschman
Skipper of S/V Windstar
Punta Rassa, Florida—352-682-2921
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Old 13-10-2012, 22:22   #2
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Location: Great Neck, N.Y.
Boat: Lancer 30, Little Jumps
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Re: engine cooling

Can speak to my experience with my 3GMC raw water cooled, bought new in 1985, have for 27 years. Critics say motor should have rusted through years ago, my Yanmar dealer/mech says
we will both be long gone and motor will be going strong.
I flush motor with Rydlyme every few years and change the 3
motor zincs,(usually do not need to be changed) again every few years. Run fresh water thru and use rust inhibit anti-freeze at end of season. Took exhaust manifold off this season just to take a look, was clean and open.
If a raw water motor is allowed to overheat, the salt will separate and line the water passages inhibiting flushing is important. That is why raw water motors runs cooler
(with a 140 degree thermostat) than a fresh water cooled motor.
Hence your hot water will be hotter with the fresh water motor.
One must flush/clean heat exchanger on fresh water system also, some remove and bring to auto radiator shop to clean.
There are no zincs in the Yanmar fresh water motors.
All in all most prefer fresh water cooled.

s/v Little Jumps
Lancer 30
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Old 14-10-2012, 04:11   #3
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Re: Engine Cooling

Fresh Water Cooled:

No salt water corrosion in head and block cooling passages.
Higher hot water temperature
Must periodically acid flush heat exchanger
Slightly more efficient due to higher operating temp

Salt Water Cooled

Calcium build up if run too hot. Must be periodically acid flushed
Lower water heat temps
Slightly less efficient

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Old 14-10-2012, 04:55   #4
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Re: Engine Cooling

there are no pros to raw water cooled engines except lower cost when new!
stop blowing smoke up my rear, blow it at the sails instead
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engine, cooling

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