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06-11-2017, 15:18
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#16
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,151
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Re: New to Salt Water - cooling systems
In my experience (one Atomic 4, one BMW D35) of raw water cooled engines operated in salt water, the problems do not come from corrosion but rather from buildup of mineral deposits in the cooling passages. For what are non-intuitive reasons (to me) mineral salts begin to precipitate from sea water if the engine temperature rises above ~165 deg F. Typically thermostats in salt water cooled engines are set around 140 deg F in order to avoid this happening, but all too often there are hot spots that exceed the stipulated temperature and precipitation begins. This sets off a cycle of higher temps/more precipitation/higher temps that can lead to complete blockage of coolant passages and eventual serious overheating problems.
Periodic treatment with acid or other descaling compounds helps avoid this blockage, but is kinda messy and mildly hazardous. I'd rather put up with the additional complexity of the secondary cooling loop than deal with the salts, and it is well established that diesel engines prefer to be run at temps higher than 165 F, resulting in longer life and better fuel economy.
A no-brainer in my view!
Jim
__________________
Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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06-11-2017, 15:26
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#17
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Registered User
Join Date: Feb 2008
Location: North Charleston, SC
Boat: Camano Troll
Posts: 5,176
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Re: New to Salt Water - cooling systems
Quote:
Originally Posted by Jim Cate
In my experience (one Atomic 4, one BMW D35) of raw water cooled engines operated in salt water, the problems do not come from corrosion but rather from buildup of mineral deposits in the cooling passages. For what are non-intuitive reasons (to me) mineral salts begin to precipitate from sea water if the engine temperature rises above ~165 deg F. Typically thermostats in salt water cooled engines are set around 140 deg F in order to avoid this happening, but all too often there are hot spots that exceed the stipulated temperature and precipitation begins. This sets off a cycle of higher temps/more precipitation/higher temps that can lead to complete blockage of coolant passages and eventual serious overheating problems.
Periodic treatment with acid or other descaling compounds helps avoid this blockage, but is kinda messy and mildly hazardous. I'd rather put up with the additional complexity of the secondary cooling loop than deal with the salts, and it is well established that diesel engines prefer to be run at temps higher than 165 F, resulting in longer life and better fuel economy.
A no-brainer in my view!
Jim
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That explains it very well.
__________________
Ron
HIGH COTTON
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06-11-2017, 15:42
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#18
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Marine Service Provider
Join Date: Sep 2014
Location: Auckland, NZ
Boat: Compass 790 , 7.9 metres or 26 ft
Posts: 2,803
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Re: New to Salt Water - cooling systems
We have a raw water cooled 1982 Yanmar diesel engine that has been used exclusively in salt water. Recently I pulled the cylinder liner ( sleeve) out to replace it & it & all internal surfaces have only minimal surface corrosion. Engine anode lasted about 2 years but we freshwater flush it when we come back to the marina but have only had this vessel for 3.5 years, the P.O. never did that. It does have a thermostat which limits it cooling water temp to about 55oC.
I could put a heat exchanger on it ( have thought about it) but after looking at how it's survived with it's existing system I dont honestly think it's worth the hassle. It's the first raw water-cooled engine I've owned apart frm outboards but I'm not scared of them anymore. However a cautionary note here. A neighbour in the marina had a sister engine that he had to junk as he never realised it had an engine anode so never changed it & his block got too corroded. It would be prudent to inspect internally if you a going to buy a salt water one in case the owner has made the same mistake.
Not sure how you would do that tho as all the internal surfaces in ours seem to be coated with a thin layer of mineral deposits. Someone else may be able to chime in here.
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06-11-2017, 16:13
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#19
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Registered User
Join Date: Jun 2013
Location: Up Qld Coast, near Yeppoon.
Boat: Passport 41, Custom Perry in steel.
Posts: 625
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Re: New to Salt Water - cooling systems
Jim is nearly right. In a engine there are many limits, in this discussion the most important temperature that needs to be controlled is the internal liner temperature, too hot and the oil doesn't do its job, too cold not efficient, dirty rings will jam up. How this is done between the 2 types of engines one with SW that is limited by the one of the salts precipitation temperature, I'd say 42DegC at a hot place, and Closed treated loop where I have seen design temperature above 105 degC. The difference is in the thickness of the cylinder liner. Both types would be targeting 180~200 degC on the liner surface.
There is a place for both types of engines, there is already enough information given by other contributors for you to make up your mind. Anything else is academic.
My preference is Closed treated Cooling system, but unfortunately my Engine also a BMW same as ex JIms the heat exchangers (2) did not come with Anodes. Quite a oversight.
__________________
Oceanrider.
"The floggings will continue until morale improves"
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06-11-2017, 16:29
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#20
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,151
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Re: New to Salt Water - cooling systems
Quote:
My preference is Closed treated Cooling system, but unfortunately my Engine also a BMW same as ex JIms the heat exchangers (2) did not come with Anodes. Quite a oversight.
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Interesting! Our old D35 had two anodes in the coolant jacket. They needed replacing every ~200-300 hours, which for us was kinda yearly. One was cleverly located behind something (forget what) that made replacement a bitch.
I lusted after converting to FWC but the BMW parts were not in our budget at the time, and I didn't have the knowledge to DIY then.
Good engine otherwise... had over 6K hours and running well when we sold her 12 years ago. Later replaced by (gasp) a Yanmar and saildrive by a (IMO) naive new owner.
Jim
__________________
Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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06-11-2017, 17:12
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#21
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Registered User
Join Date: Jun 2013
Location: Up Qld Coast, near Yeppoon.
Boat: Passport 41, Custom Perry in steel.
Posts: 625
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Re: New to Salt Water - cooling systems
Sorry about thread drift, but to Jim mine is a D50, I have since retrofitted anodes to both oil and Jacket system by installing SS fittings and bonding wires.
It kind of makes sense that a thermostat for a SW system must be different temperature than JCW system. If somebody was so mistaken to change a JCW system over to SW cooled it wouldn't last long it hasn't got anodes but worse still the thinness of the cylinder wall would soon corrode away. The other way, well you'd have to keep it cool similar to SW cooled engine otherwise the internal liner temp would be too high to carry the very slim and already hot, oil film.
__________________
Oceanrider.
"The floggings will continue until morale improves"
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07-11-2017, 05:40
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#22
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Registered User
Join Date: Mar 2013
Posts: 7
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Re: New to Salt Water - cooling systems
Diesel engines want to run at higher temperatures, 180+ degrees F. If you use a 180 thermostat in a salt water cooled open engine salt will percipate from the salt water and quickly clog engine cooling passages. Hence, salt water cooled open systems typically use thermostats that run below 160 degrees F. Never run thermostats meant for closed systems in a raw water system, especially in salt water. An added benefit to closed systems is that hot water heaters are circulating water much hotter than raw water systems and you're not circulating salt water into your water heater. The fact that virtually every marine diesel manufactured today is closed loop has to tell you something. In the short term open systems are fine as it takes many years for salt to take its toll but any open diesel found today is most likely quite old. Salt corrosion to a heat exchanger is much easier and less expensive to deal with than corrosion in a block, head, and even your salt water cooled marine gear. I had an old Volvo MD7A which has an open system with raw water cooled transmission. The raw water comes from the ocean into the transmission then up to the raw water pump where it circulates through the engine. I was destroying impellers at a fast clip. The culprit turned out to be scale in the transmission breaking free and traveling through to the raw water pump quickly destroying the Impeller. Raw water strainer is before the transmission. Most handy diy type sailors are capable of cleaning or replacing a heat exchanger, tearing a block apart, not so much. A 20 year old salt water cooled diesel is a problem waiting to happen.
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07-11-2017, 05:51
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#23
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Registered User
Join Date: Mar 2013
Posts: 7
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Re: New to Salt Water - cooling systems
Quote:
Originally Posted by Jim Cate
In my experience (one Atomic 4, one BMW D35) of raw water cooled engines operated in salt water, the problems do not come from corrosion but rather from buildup of mineral deposits in the cooling passages. For what are non-intuitive reasons (to me) mineral salts begin to precipitate from sea water if the engine temperature rises above ~165 deg F. Typically thermostats in salt water cooled engines are set around 140 deg F in order to avoid this happening, but all too often there are hot spots that exceed the stipulated temperature and precipitation begins. This sets off a cycle of higher temps/more precipitation/higher temps that can lead to complete blockage of coolant passages and eventual serious overheating problems.
Periodic treatment with acid or other descaling compounds helps avoid this blockage, but is kinda messy and mildly hazardous. I'd rather put up with the additional complexity of the secondary cooling loop than deal with the salts, and it is well established that diesel engines prefer to be run at temps higher than 165 F, resulting in longer life and better fuel economy.
A no-brainer in my view!
Jim
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Spot on. And the more precipitate that accumulates the more hot spots will be created. Raw water engines are fine until they're not. Regular back flushing before issues arise would greatly extend the life of the engine how many of us do that? Outboards are mentioned. Any mechanic will tell you that an outboard used exclusively in fresh water will outlast a salt water outboard by many years.
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07-11-2017, 17:47
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#24
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Registered User
Join Date: Feb 2014
Location: Palm Coast Florida
Boat: 2018 Seadoo GTX 230
Posts: 1,059
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Re: New to Salt Water - cooling systems
Are there any aluminum block engines to help offset salt water corrosion? Most auto engines are now some sore of aluminum alloy. That should have filtered into the boating industry.
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07-11-2017, 18:16
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#25
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Registered User
Join Date: Sep 2009
Location: Houston
Boat: ‘01 Catana 401
Posts: 9,626
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Re: New to Salt Water - cooling systems
Quote:
Originally Posted by tuffr2
Are there any aluminum block engines to help offset salt water corrosion? Most auto engines are now some sore of aluminum alloy. That should have filtered into the boating industry.
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Ummmm outboards?
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07-11-2017, 22:10
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#26
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Marine Service Provider
Join Date: Sep 2014
Location: Auckland, NZ
Boat: Compass 790 , 7.9 metres or 26 ft
Posts: 2,803
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Re: New to Salt Water - cooling systems
Quote:
Originally Posted by spflyer
Diesel engines want to run at higher temperatures, 180+ degrees F. If you use a 180 thermostat in a salt water cooled open engine salt will percipate from the salt water and quickly clog engine cooling passages. Hence, salt water cooled open systems typically use thermostats that run below 160 degrees F. Never run thermostats meant for closed systems in a raw water system, especially in salt water. An added benefit to closed systems is that hot water heaters are circulating water much hotter than raw water systems and you're not circulating salt water into your water heater. The fact that virtually every marine diesel manufactured today is closed loop has to tell you something. In the short term open systems are fine as it takes many years for salt to take its toll but any open diesel found today is most likely quite old. Salt corrosion to a heat exchanger is much easier and less expensive to deal with than corrosion in a block, head, and even your salt water cooled marine gear. I had an old Volvo MD7A which has an open system with raw water cooled transmission. The raw water comes from the ocean into the transmission then up to the raw water pump where it circulates through the engine. I was destroying impellers at a fast clip. The culprit turned out to be scale in the transmission breaking free and traveling through to the raw water pump quickly destroying the Impeller. Raw water strainer is before the transmission. Most handy diy type sailors are capable of cleaning or replacing a heat exchanger, tearing a block apart, not so much. A 20 year old salt water cooled diesel is a problem waiting to happen.
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Not sure you are right. There are plenty of raw water cooled diesels around that are 35+ years old . BUT YOU HAVE TO KEEP ANODES TO SPEC. Can't comment on your volvo design as i havent had one. But yes I can see it mite be a problem if the salt water goes thru trans 1st. You cant tar all raw water cooled engines with the same brush tho. We have a 3.5 yr old impeller in our raw water cooled !982 Yanmar YSM8 & we do btwn 2-300 hrs per year. I'm not supporting Yanmar here. I dont like the predatory parts pricing policies & would prefer a Kubota based engine & dont like the exhaust design on our YSM8 but I haven't been able to blame the raw water cooling for any of the engine issues. Can't comment on the fuel efficieintcy & oil life issues as I didnt convert ours to fresh water cooled. Not looking for an argument, just relaying our experience. Glad you posted yours, it gives me something to consider other than Volvos parts pricing if I look at another Volvo powered yacht ( sailboat in American speak). Good reading on these forums
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