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Old 24-01-2010, 14:21   #1
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Fresh vs Salt Water Engine Cooling

I have heard some pros and cons for saltwater cooling of a diesel. My Harstad uses saltwater.

I'd love to hear opinions on maintenance/issues with each.

Tom
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Old 25-01-2010, 04:13   #2
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Not sure what you mean by salt water cooling?
Do you mean running the salt water through the ports in the engine block instead of through a heat exchanger?

I looked up your boat and it is unusual...I was surprised it was trailer-able.
Do you trailer it?
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Old 25-01-2010, 04:31   #3
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Have salt water cooled also. Have a one way valve hooked up to fresh water tanks, and in line from seacock. When I finish motoring, Turn off Saltwater and flush with fresh. I carry 340ltr in fresh water tanks. Consider the engine important so I don't shower often. Engine is 1978 10hp Bukh that's been rebuilt/serviced once, about 400hrs ago.
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Old 25-01-2010, 05:54   #4
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raw water cooling

The principal problem is corrosion and salt buildup in the cooling system. Too reduce the salt buildup, raw water cooled engines often have higher flow rates and thus run at lower temperature, which is less efficient. The disadvantages to fresh water cooling are higher cost, more complex cooling circuit (two pumps and a heat exchanger), and a slight possibility of leaks or plugging up in the heat exchanger.
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Old 25-01-2010, 07:01   #5
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A: call it "raw water cooled" (instead of salt water cooled), to distinguish it from a "closed loop/heat exchanger" system. You see, if you are in a fresh water lake, your "salt water" system would be using fresh water. So, to say "raw water" means that everyone understands you are referring to a system that uses cooling water that comes from outside the boat, be it salt of fresh. The water that surrounds a the engine block in a closed loop/heat exchanger system is commonly referred to as "fresh water".

The main problem with raw water cooling in a salt water environment is that the salt will begin to leach out of the water at about 160deg F. Most marine motors, especially diesel ones, want to run up around 180-190deg F. If you try and use salt water as a coolant at that temp the water channels inside the motor will eventually get clogged with salt/mineral deposits. The other choice is to run the motor at a lower temp, but with diesels, you invite all manner of other issues related to running too cold.

There are thousands of boats that are sailed in fresh water and are using raw water as a coolant without problems, except one: You will not be able to add any anti-freeze to your block, which these days has lots of other good additives that help keep things lubricated etc inside the water jacket of the motor. Not to mention what happens if you live in a cold climate.

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Old 25-01-2010, 07:36   #6
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I have a Yanmar 18hp raw water cooled motor in my monohull. The motor is now 21 years old. I have never flushed it with fresh water but have changed the anodes every year. The motor runs like a dream and has never let me down. It even still looks new from the outside and has never been rebuilt. The boat is based in Cape Town and has always been used in the sea.
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Old 25-01-2010, 07:47   #7
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I have a Yanmar 18hp raw water cooled motor in my monohull. The motor is now 21 years old. I have never flushed it with fresh water but have changed the anodes every year. The motor runs like a dream and has never let me down.a.
Do you know what temperature it runs at? Or, what temp thermostat is installed? A common solution is to run a 160deg Thermostat. For such a small hp motor, running a little cold isn't gonna affect much. Or perhaps the info about salt deposits is just wrong... I'm always learning.
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Old 25-01-2010, 07:55   #8
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I am not sure at what temp it runs, I do know it does have a different thermostat to the motors with a freshwater system. I do remember hearing that if it runs too hot you can get salt deposits in the motor. For my powerboat I use salt-away that dissolveds the salt and leave a form of protective coating. I am sure one could put some in the strainer once a year to make sure there is no salt build up.
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Old 25-01-2010, 08:02   #9
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I use salt-away that dissolveds the salt and leave a form of protective coating. I am sure one could put some in the strainer once a year to make sure there is no salt build up.
You're probably correct, the salt issue can be dealt with in a number of ways. What about just general galvanic corrosion inside the motor? Certainly, a fresh water system has the edge there.

There is no work-around for the anti-freeze issue for boaters in cold climates, other than to haul and drain until warmer weather returns.

Just so the OP has some pros and cons, thats all.

Doug
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Old 25-01-2010, 08:28   #10
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There are three basic ways to handle raw water cooled engines in freezing climates. 1. pull and winterize them; 2. shut your intake valve and run antifreeze through the sea strainer or y-valve; 3. install an engine room heater.

It has to get pretty cold for a salt water boat to run into trouble with freezing. Sea water freezes at 28F, but the water your boat sits in is often much warmer than that, providing you with some protection down to ambient temperatures in the low 20's. Of course if you're betting on not freezing and you're wrong...

Brett
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Old 25-01-2010, 14:59   #11
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I've had several raw water cooled Yanmars over the past fifteen years.
There are lots of pro's including less moving parts, the engine bay area is significantly cooler, ect.
The only con. In my opinion is not having the ability to heat water from the exchanger. If memory serves me correctly the Yanmar raw water thermostats opens at 140 degrees.
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Old 25-01-2010, 15:23   #12
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The only con. In my opinion is not having the ability to heat water from the exchanger. If memory serves me correctly the Yanmar raw water thermostats opens at 140 degrees.
Bill,
We have a 20 year old volvo 2003 raw water cooled 3 cylinder 28 h engine. Runs very well, had a decoke last winter but no other major problems. Heats the calorifier in about 40 minutes of engine running.

However running a couple of gallons of freshwater doesn't desolve salts that have crystalised. In 1995 I used a Yam 115 outboard for a week on a river (the engine normally runs in saltwater) returning home she was due a major service. Out came the thermostats and I was astonished to find salt crystals still present after a week of freshwater use.

You could argue that engines wear out the components before saltwater causes there demise.

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Old 25-01-2010, 16:19   #13
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You could argue that engines wear out the components before saltwater causes there demise.

Pete
One could argue that but would likely be wrong Exhaust manifolds are usually the first to go
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Old 25-01-2010, 19:14   #14
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One could argue that but would likely be wrong Exhaust manifolds are usually the first to go
I agree. I had a raw water cooled Bukh DV20. That engine is built like the proverbial brick s**t-house, but after twenty-odd years the manifold and the thermostat housing were beginning to show holes. The salt and scale build-up were also evident. The Bukh weighs about 220 kg compared to 120 kg for the same horsepower Yanmar 3YM20. I don't think the 3YM20 would last very long with raw water cooling (unless the raw water was fresh!)
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