Corrosion pundits - what about flushing with fresh water?

[DDW]

I intend to flush the engine and genset raw cooling systems with fresh water when I leave the boat, and when it is hauled. Since the systems are still flooded, it would seem like the zinc pencil anodes would be ineffective. Many pundits are now recommending aluminum as the best choice for both salt and fresh, so it seemed like changing everything over to aluminum would solve the problem - but I'm having a hard time finding aluminum (no time to mail order).

Perhaps a further complication is I will winterize using pink antifreeze. This is supposed to have some corrosion inhibiters in it, hard to know what they do. I think most everyone who winterizes in salt water country just leaved the zincs in.

Any experts out there want to chime in?

 

[dhays]

I'm not an expert, but I believe that the antifreeze will help protect again oxidative corrosion. The anodes help protect against galvanic corrosion. Two different processes. Since the antifreeze would, I assume, be about the same as fresh water as far as an electrolyte I don't think it would make much of a difference.


Another question, and I don't know the answer as I am an idiot, but if you are putting the boat on the hard for the winter, do you need to worry at all about galvanic corrosion? The boat won't be immersed in an electrolyte...? Now, having said that I know that the Statue of Liberty had really bad galvanic corrosion and she wasn't swimming.

 

[Bacchus]

Ddw
I got very quick delivery from Precision Metals. They will either sell direct (if no dealers) or let you know who in your area handles their anodes.
My thought is even though boat is not immersed in water... so no need for external running gear anodes... the water cooling system is still flooded and susceptable to galvanic corrosion.
But I am no expert either... maybe others know more / different.

 

[DDW]

Yes, it's the cooling systems I'd be concerned with. The running gear would be dry (and there isn't much on this boat anyway). I know there is galvanic corrosion in automobile cooling systems, different metals in an electrolyte - even fresh water is an electrolyte unless deionized, and antifreeze is somewhat conductive normally. I know when I buy it for the tig welder I have to buy the expensive non-conductive stuff. A major challenge for antifreeze producers is the anticorrosion package to protect against corrosion. RV/Marine pink has some, but maybe not much, guessing from the price.

But the question goes beyond winter layup - I'd want to fresh water flush the cooling system when the boat is left for any length of time, even floating. And if the answer is aluminum pencil anodes, then I assume I'd also want aluminum running gear anodes since they are electrically connected and should have the same galvanic potential.

 

[boatpoker]

Only metals in contact with and through the electrolyte are at risk of galvanic corrosion i.e. the cooling system. If you flush with fresh water, your zinc anodes in the cooling system are useless as zinc does not have sufficient voltage potential to overcome the lower conductivity of fresh water.

 

[what_barnacles]

be careful flushing when the motors are off.

 

[kchace]

I and most folks up here in the NE flush with the pink stuff that says it has anti-corrosion qualities and call it done. Do it with the engine running and use enough and you do not have to drain your water lift muffler (assuming that is what you have).


In the spring replace internal anodes with new - get aluminum if you can.



Ken

 

[kchace]

Another question, and I don't know the answer as I am an idiot, but if you are putting the boat on the hard for the winter, do you need to worry at all about galvanic corrosion? The boat won't be immersed in an electrolyte...? Now, having said that I know that the Statue of Liberty had really bad galvanic corrosion and she wasn't swimming.

The problem the OP brings up is in regards to the raw water parts of the cooling system. Typically they stay full (unless drained). Internal zincs are there because of dissimilar metals inside the cooling system which can certainly keep corroding due the system still being full of water - whether the boat is in or out of the water.


Ken

 

[RT Firefly]

Greetings,
Mr. kc. "...due the system still being full of water..." Not full of water IF you flushed with the "pink stuff". I guess the question arises about the conductivity of the "pink stuff" and the composition and necessity of the anodes over the winter.

 

[dhays]

The problem the OP brings up is in regards to the raw water parts of the cooling system. Typically they stay full (unless drained). Internal zincs are there because of dissimilar metals inside the cooling system which can certainly keep corroding due the system still being full of water - whether the boat is in or out of the water.


Ken

Thanks Ken. That makes sense and now that I think about it, it seems obvious.

 

[DDW]

The pink stuff has a lot of water in it, and is an electrolyte itself. It does not completely displace the existing water in the cooling system, but mixes with it. So the possibility of galvanic corrosion exists. While it does not seem to cause a problem with salt water boats and zinc anodes, or fresh water boats and magnesium anodes, the question remains what about fresh water boats and zinc anodes? I don't think there is a lot of collective experience there, as it is an unusual situation.

 

[kchace]

Greetings,
Mr. kc. "...due the system still being full of water..." Not full of water IF you flushed with the "pink stuff". I guess the question arises about the conductivity of the "pink stuff" and the composition and necessity of the anodes over the winter.

Yes. I think we're in violent agreement on this...

 

[caltexflanc]

If you are in San Francisco I can't think of any reason to winterize the boat, or flush the raw water side with fresh water for that matter. The bay is an estuary and as you work your way up the Delta, salinity decreases. And boats have been successfully using zincs in Norcal for decades, BTW.

Now I have to say, having cruised for several years out here on the east coast, I never met anyone who flushed their raw water side with fresh water ever, other than via a trip up the Hudson or Connecticut or Merrimack rivers...

What am I missing here?

 

[RT Firefly]

Greetings,
Mr.c. " What am I missing here? " Climate change perhaps?

 

[kchace]

Now I have to say, having cruised for several years out here on the east coast, I never met anyone who flushed their raw water side with fresh water ever, other than via a trip up the Hudson or Connecticut or Merrimack rivers...

What am I missing here?

Gotta agree. Flush what?

 

[TDunn]

I always just run pink antifreeze through the system until it is coming out the exhaust. This is done by running the engine with the hose to the strainer in a bucket of antifreeze. When I am getting antifreeze out the exhaust I run another gallon or two through then shut down. I change my zincs in the spring before launch and I have never had any corrosion issues, but I have only been doing it this way for the last 23 years. I am in Maine.

 

[DDW]

I am near SF, but the boat is in Canada. Yes it freezes there.

Corrosion issues from salt water aren't unique to me. I've taken boats from fresh to salt water and the corrosion begins immediately. Flushing with fresh water is a preventative measure, not perfect but I hope helpful. Standard procedure for example on outboards laid up for the winter. Why do they bother? The boat came to me with fresh water flush fittings and capability and I'd like to use it.

Now I've never flushed any of the boats I've had in the past - but there have been corrosion issues for sure. Exhaust elbows rusting, heat exchangers plugging up with salt and corrosion, etc.. Actually I've rarely heard of anyone NOT having at least some of these problems.

You'all are talking about taking a boat out of salt water, flushing a little antifreeze through it, and leaving the zincs in the resulting mixture. What I'm talking about is a bit different, and the results might be as well. I'll flush with fresh water for 15 minutes or more, not just a couple of gallons of pink, so most of the salt water really will be gone. Then follow with pink. Corrosion still happens in fresh water, just not as aggressively. That's why they sell anodes for fresh water.

 

[firehoser75]

DDW and others,
Flushing your raw water side (often) with fresh water is a good way to help "stave off" marine age (basically the ravages of corrosion in the salt (air and water) environment that our salt water operated boats live in). If you flush regularly with fresh water (and store the raw water cooling side cleaned of salt water), you can greatly extend the time between having to fully service the various heat exchangers, gear coolers, aftercoolers, etc. and avoid the probability of overheating your engine (at least better of odds of doing so). Salt water in a hot environment (like inside our engine's components) will form a limestone like substance in the cooling passages which will only be removed (once hardened) by relatively aggressive measures like sending out to the rad shop for acid cleaning. Fresh water flushing will increase the time intervals between this type of (costly and/or time consuming) servicing. I just took apart my aftercooler for routine servicing (after 2 full seasons and about 400 engine hours) and there was no corrosion (even though the cooler consists of a "dog's breakfast" of dissimilar metals), and no calcium buildup at all. After properly reassembling with lots of grease, I can now leave this component for 4-5 years before servicing again, instead of having to look after it every 2-3 years. By the way, I service the cooling system more often than I could possibly "get away with", but I would rather be on the safe side. As far as zincs are concerned, I am certainly not an expert on this area, but I trust Tony Athens of Seaboard Marine. Unless I am reading his advice on this incorrectly, he says stay with zinc even if flushing with freshwater. His website has tons of great, free advice based on his training, education, and many years of experience. By the way, I am not associated in any way with him, or his business, just a grateful boater! His website is: sbmar.com.
Hope this info proves helpful,
Tom

 

[DDW]

I can't see how a fresh water flush would hurt, certainly. Where do you see Athens saying zinc even if flushed? Haven't found that in his stuff. I'd be interested in his thinking.

 

[boatpoker]

Zinc anodes simply do not work in fresh water. Their voltage potential is not high enough.
In fresh water a zinc anode very quickly develops a coating of zinc hydroxide and sometimes a calcareous coating, both of which insulate the anode and prevent any current flow, thereby rendering them useless. This is all well established scientific fact ..... Google it.

 

[firehoser75]

Too Much on Site to Remember exactly

I can't see how a fresh water flush would hurt, certainly. Where do you see Athens saying zinc even if flushed? Haven't found that in his stuff. I'd be interested in his thinking.

Sorry, but between his responses on forum inquiries and all of the material he has posted on his site, I cannot remember exactly where I read it. If you want to be sure of his opinion, either ask the question on his site's Cummins forum or send him a personal email. I am reasonably sure he will respond.
Not a definitive answer in and of itself, but my aftercooler was stored all last winter with a solution of salt away and freshwater in it (with zincs), it was run almost 400 hours over 2 seasons and when I just took it apart there was no corrosion at all and only a very tiny amount of calcium showing around some of the core tube openings. A very tiny amount. I also freshwater flushed the engine as often as I could during the summer season. By the way, the gear cooler looked very clean and corrosion free as well.
If nothing else, read Tony's advice on aftercooler maintenance. They can cost you pretty dearly if you don't do the maintenance.
Regards,
Tom

 

[clyde]

hmmm...flushing with fresh water, and aluminum anodes. i read the hype, so i tried aluminum anodes one time, and when we hauled out, i found prop and thru hull problems! so quickly went back to the zink anodes! [after some conversations with people smarter than me] as to freshwater flushing, i`ve been doing it for eons! have gotten friends to do it too...if our boat is going to sit for a week or more, it gets flushed! my cooler zinks last more than a yr! when i was commercial fishing, when the season was over at the end of november, we took them into lake union/fresh water for several weeks, to let the growth fall off the hull! all commercial boats have keel coolers, so it`s a closed system like car...clyde

 

[KiwiClive]

I added a system where I plug in the water hose from the dock and turn on a few valves and flush the engines/genset with water and then a soapy soultion.
Works well.

 

[DDW]

Since I couldn't find aluminum anodes, I flushed with fresh water, then pink antifreeze, and went home.

I wonder what a solution of PG antifreeze and fresh water does to the galvanic series.

 

[Albin]

Zinc anodes may or may not be effective in fresh water but it doesn't matter because if your boat is in Canada as mine is (Nova Scotia), you have to flush the system with the pink plumber's antifreeze - no option. Even salt water will freeze and burst a heat exchanger on the coldest days in winter in all parts of Canada except for BC. With regard to the fresh water flush which includes the main engine/generator heat exchanger, the muffler system (assuming a wet exhaust), and the feed line(s) to your dripless seal (assuming no stuffing box), there is definitely a benefit of getting the salt water out before you put in the plumber's antifreeze. On my boat that is a simple operation because I have my engine and generator plumbed into my freshwater tank so all I have to do is close the main raw water intake and open the fresh water supply valve and run tn the engine for a few minutes to clean out the system. I even do this numerous times throughout the summer if I know the boat is going to be laid up for more than a day or two. It greatly reduces internal corrosion and it takes about 2 minutes.

When pouring the plumber's antifreeze into your strainer, it's best to suck the salt water out of there first with a shop vac so the anitfreeze isn't initially diluted. Don't skimp on the antifreeze - pour at least 8-10 liters in there until red liquid can be seen coming out the exhaust and the around the prop shaft if you have a dripless seal. Don't forget to spray fogging oil into your air intake before you shut of the engine. Don't delay between these steps because you don't want your raw water impleller to run dry for more than a minute or so while you do the fogging. Your engine will then be properly pickled. Good luck.

Cheers, Jeff

 

[boatpoker]

Zinc anodes may or may not be effective in fresh water

There is simply no question that zinc does not work in fresh water. The science is irrefutable.

The photo below shows a magnesium anode and a zinc anode on the same shaft after a season in the fresh water of Lake Ontario. The zinc anode clearly shows no galvanic effect while the magnesium shows definite galvanic corrosion.

 

[DDW]

I do not currently have a connection between fresh water tank and the flush fittings on the engine and genset. I think I may put them in, as it occurs to me it would make draining the fresh water tank much quicker. Also eliminate the need to get a hose to the engine room.

On the galvanic thing, the electrolyte makes a difference in what anode you use, e.g., fresh water vs. salt. So what's the right answer for PG? I guess I should have paid attention in chemistry class all those years ago but at the time it bored me to tears.

 

[Trawler Dave]

Zinc anodes in fresh water

You may be right about Zinc not having the voltage potential to carry current in fresh water. This may be true when fresh water is defined as distilled water. The fresh water WE boat in has plenty of contaminants to carry a current. The evidence is the fact that I need to change my zincs every other year. I see them rot away just exactly as they did in salt water, albeit slower.

 

[DDW]

The only thing I have been able to find so far is troubling: most of the info is from closed cooling loops, which are typically charged with a mixture of water and glycol (either ethylene or propylene). Dow in their literature cautions to avoid using galvanized metals in these systems, because in glycol the galvanic positions of steel and zinc are reversed, that is zinc becomes cathodic to steel. In plain language the steel corrodes to protect the zinc. Now these antifreezes have corrosion inhibiters in them, but again there are cautions that this will slow but not stop galvanic corrosion.

 

[boatpoker]

You may be right about Zinc not having the voltage potential to carry current in fresh water. This may be true when fresh water is defined as distilled water. The fresh water WE boat in has plenty of contaminants to carry a current. The evidence is the fact that I need to change my zincs every other year. I see them rot away just exactly as they did in salt water, albeit slower.

Sorry, still wrong. Pure water is not conductive at all. Fresh water for the purpose of cathodic protection is neither defined as pure nor distilled water. All voltage potentials as measured for all cathodic protection systems are made with a range of contaminants normally found in lake water.

Suggest you study the NACE or ABYC Standards for cathodic protection which can explain all this in detail.