fresh water flush

[magna 6882]

I have read some recommendations to flush the main engine with dock water after use.I see some water connections that utilize the sea strainer but mine in not easily reached so i was thinking of adding a T and running a hose to the stern to make the flush easy.
Before i go to far i wanted to get your thoughts regarding the value.Do many of you flush?
I can see times when my boats sits for several weeks and the cooling system full of salt should be more damaging then fresh?
can i get your collective thoughts.
Thanks

 

[Comodave]

It is certainly a big benefit to flush with fresh water. Check out Tony Athens thoughts on it at sbmar.com. As to exactly how to hook it up would depend on the individual setup.

 

[magna 6882]

I do see the benefit but am curios as to how many folks do it. I have never seen anyone doing it.

 

[TJM]

Closed loop cooling or sea water thru the entire engine - raw water cooling ?
Water pressure will need to be controlled as to not blow out anything.
Your zinc anodes may have a different opinion on the matter.

 

[Comodave]

If you do start flushing with fresh water then I would recommend you use aluminum anodes because if you have zinc anodes they don’t work in fresh water. And your engine will be sitting with fresh water for long periods.

 

[firehoser75]

Magna,
I am no longer a boat owner, however, when I did own Pilitak, I freshwater flushed the engine everytime I had access to a good flow of dock water. Some marinas, especially in the Broughtons, did not have a decent flow of dock water, therefore, no flush then.
The benefits are well established, but most boaters do not do it. I guess (but can't read minds) that they either think it is too much work (can't be bothered), have unfounded fears about "problems" (eg. old wives tales), or just don't know anything about it?? According to Tony Athens over on sbmar.com, regularly FW flushing will extend the time between needed servicing of your engine's cooling system (by as much as doubling it), will keep your engine running cooler longer thereby reducing the likelihood of an overheat, and will reduce the natural "marine aging" that happens to your engine even when not running.
The downsides: it does take some time (for me about 10 minutes total from start to all put away), it may initially take some planning and setup (depending on the boat and it's setup), and you have to idle at the dock for about 5 minutes (most setups, some don't have to run the engine). You will have to change from zinc anodes to aluminum for the engine if you FW flush to ensure ongoing protection from corrosion.
Personally I think the time spent is well worth it, as off engine servicing of the cooling components (aftercoolers need servicing more often), can be delayed by serveral years saving lots of time and/or money (if paying a pro) over the long run, and your cooling system will be kept in better condition between services providing (potentially) added protection (and longevity) to your engine.
However, it is a personal choice.
Good luck.

 

[DavidM]

I added a fresh water flush to my Yanmar 6LY. It certainly extended the life of the engine zincs from 6 mo to a year+ between changeouts. But did it eliminate corrosion in the various exchangers? I doubt it.

David

 

[firehoser75]

Zinc anodes will "coat over" when exposed to freshwater. So if you freshwater flush or moor or travel in freshwater, you need to switch the (engine) anodes to aluminum to ensure ongoing protection in both salt and fresh water (hull anodes as well if moored in freshwater). It is my understanding, that once coated, for a zinc material to "regain" it's protection properties, it must be physically "scrubbed" to remove or reduce this coating, otherwise the zinc does not "sacrifice" itself to protect the other metals, hence their longer "life" (because their effectiveness is reduced).
Will FW flushing "eliminate" corrosion, no one said it would. Reduce........ probably. Saltwater is well known to be much more corrosive than fresh. Why do people with boat trailers take the time to rinse off their trailers and pickups and flush their outboards after saltwater exposure? Certainly in any areas where you have saltwater surrounding dissimilar metals, by changing the water to fresh it will reduce electrolytic corrosion (the battery effect). Saltwater is a much more effective electrolyte compared to fresh, allowing one metal to become the anode while another becomes the cathode. Regular FW flushing will also reduce the build up of salt like deposits throughout the system allowing more effective cooling.

However, to each his own, and everyone will put their efforts where THEY think the best "value" is.

 

[sunchaser]

It may depend on where the vessel is located. Our vessel in cool BC waters never was flushed. The 6 different heat exchangers never showed any unusual fouling (AC, main engines heat exchangers, genset or transmission coolers).

 

[magna 6882]

If the boat was going to sit for a few months would it be better to just drain the aftercooler? We usually travel south in the winter while the boat sits in seattle.

 

[TBill36]

Zinc anodes will "coat over" when exposed to freshwater. So if you freshwater flush or moor or travel in freshwater, you need to switch the (engine) anodes to aluminum to ensure ongoing protection in both salt and fresh water (hull anodes as well if moored in freshwater). It is my understanding, that once coated, for a zinc material to "regain" it's protection properties, it must be physically "scrubbed" to remove or reduce this coating, otherwise the zinc does not "sacrifice" itself to protect the other metals, hence their longer "life" (because their effectiveness is reduced).
Will FW flushing "eliminate" corrosion, no one said it would. Reduce........ probably. Saltwater is well known to be much more corrosive than fresh. Why do people with boat trailers take the time to rinse off their trailers and pickups and flush their outboards after saltwater exposure? Certainly in any areas where you have saltwater surrounding dissimilar metals, by changing the water to fresh it will reduce electrolytic corrosion (the battery effect). Saltwater is a much more effective electrolyte compared to fresh, allowing one metal to become the anode while another becomes the cathode. Regular FW flushing will also reduce the build up of salt like deposits throughout the system allowing more effective cooling.

However, to each his own, and everyone will put their efforts where THEY think the best "value" is.

Where can you buy aluminum pencil anodes for engines? I just recently installed a fresh water sytem and want to change over. Can find magnesium and zinc, but not aluminum in pencil style.

 

[psneeld]

There are several You Tubes I have watched and tons of reports from mechanics that are mostly in favor of it but yet they do say it doesn't do anywhere near the effect most people think it has. Even tests with products designed to remove salt like "Salt Away" have very limited results.

As normal, certain conditions and certain engines can have a lot to do with the variation.

My experience with all sorts of engines seem to confirm this. I have seen outboards religiously flushed that still show corrosion in nooks and crannies where water sits (probably fresh water from flushing but the aluminum block corrodes fast with just running in salt I guess). I know of gas and diesel inboards that run decades without flushing that seem no worse for the wear than some that people flush.

I will say that if you have salt water fed coolers (oil/engine/after) it probably isn't a bad idea, but those I have limited experience seeing inside of. Those that I have that are monel seem pretty good, but others not so much. Usually if you have an engine that has been around awhile, there is a history of premature failures and recommendations for regular flushing.

 

[psneeld]

Where can you buy aluminum pencil anodes for engines? I just recently installed a fresh water sytem and want to change over. Can find magnesium and zinc, but not aluminum in pencil style.

If regularly flushing with fresh water and limited hours running in salt, magnesium would probably be fine with close watching for wasting as they will be the quickest to waste.

Not sure about the need to switch though.... many of the places the anodes are may self drain enough the anodes are not fully sitting in fresh water continuously. If the boat is used regularly, not sure any significant "coating" occurs as my Lehman has spent months in fresh or slightly brackish (where aluminum would be recommended) and because I was back in salt soon enough, without any other maintenance on the zincs, the worked fine with normal wasting rates. Again, may be engine/situation dependant.

 

[mvweebles]

Be careful with pressurizing your raw water intake line. Your only defense against flooding your wet exhaust and drowning your engine is the impellor on your raw water pump which makes a decent seal, but the system is not designed with pressurized water in mind.

Peter

 

[lwarden]

I'm pretty religious about fresh water flushing. Now that I have all the raw water cooled parts in perfect shape I want to keep it that way. I had to replace an after cooler and that was an expensive item....
To prevent overpressure I plumbed a hose connection in the cockpit into the engine room where it is teed three ways, one to each engine and one to the sea strainer for the AC cooling line (generator would work too). The line running to the AC has a check valve with a low cracking pressure. There are ball valves at the entrance to each sea strainer which is opened when flushing only. The check valve going to the AC prevents over pressurizing the engine raw water pumps. When flushing I close both engine seacocks and leave the AC cooling open. Then I turn on the hose, run each engine then shut the water off and open the seacocks. The process takes 10 minutes and only two trips to the engine room.

 

[psneeld]

Because I have heard that cold water flushing is pretty ineffective bit still a bit valuable... many references I have seen including my new outboard manual suggests 15 minutes (per engine) and I often let it go longer. Believing if even 15 minutes may or may not help that much a little more might be a little better.

 

[lwarden]

Because I have heard that cold water flushing is pretty ineffective bit still a bit valuable... many references I have seen including my new outboard manual suggests 15 minutes (per engine) and I often let it go longer. Believing if even 15 minutes may or may not help that much a little more might be a little better.

The point is to remove the salt water from all raw water filled cavities since salt water is a far greater conductor, therefore, electrolysis is dramatically reduced. This only takes a minute or two so no need to do it for 15 minutes. Our engines are far different from outboards and don't have raw water controlled thermostats. I don't know who told you it's ineffective, I would totally disagree based on my experience with it on my past few boats. Tony Athens would disagree as well....

 

[psneeld]

The point is to remove the salt water from all raw water filled cavities since salt water is a far greater conductor, therefore, electrolysis is dramatically reduced. This only takes a minute or two so no need to do it for 15 minutes. Our engines are far different from outboards and don't have raw water controlled thermostats. I don't know who told you it's ineffective, I would totally disagree based on my experience with it on my past few boats. Tony Athens would disagree as well....

It's generally ineffective to wash away salt buildup if it has already crystalized but if it's electrolysis you are mainly worried about I haven't seen that as a big issue and I have worked with several commercial operations that never flushed and few boaters I know except outboard owners do it either.

As I said though it doesn't hurt to do it and maybe it does help.

 

[boomerang]

Our last boat had a Perkins with a cast iron raw rater exhaust manifold and riser. I religiously flushed it but did so because of the cast iron components. I wasn't so much concerned with the cupronickel oil cooler. Same thing with our current boat ,although it has a Lehman engine with the exhaust manifold being part of the closed cooling system. I still flush it after each use ,mainly to help save the cast exhaust riser. The boat is sitting in pretty much fresh to brackish water now and I don't flush it after each use now because I got thinking that the slightly chlorinated dock water was worse for the parts than the brackish water was. I'm not too much worried about the engine zinc in fresh water because if I'm using it in fresh water it doesn't need to be protected anyway. I never have seen that the zincs needed scrubbing after being immersed in fresh water to remove any coating; they still looked like they were doing their thing when I returned to boating in saltwater. The same goes for the boat zincs. I'm certainly not jumping overboard to scrub the shaft and rudder zinc just because they've been used in fresh water!

 

[firehoser75]

One provider of aluminum engine anodes (no relationship other than I ordered from them a few times):
https://performancemetals.com/pages/navalloy-aluminum-anodes

 

[Comodave]

As to the effectiveness of freshwater flushing, I just rebuilt my aftercoolers. They are 25 years old and have never been serviced. They had some corrosion in the cores. But they have been in freshwater their whole lives. Does anyone think that in saltwater for 25 years they would still be working without any servicing. Probably not. So if my boat was kept in saltwater I absolutely would be flushing the engines.

 

[TBill36]

Be careful with pressurizing your raw water intake line. Your only defense against flooding your wet exhaust and drowning your engine is the impellor on your raw water pump which makes a decent seal, but the system is not designed with pressurized water in mind.

Peter

Over on boatdiesel one of the subscribers blew out the waterpump seal when pressuring with freshwater with the through hull ball valve closed and engine not running. Probably no reason to ever flush with the through hull closed as the fresh water flow will offset most if not all incoming raw water - at least at idle for anything under 1000 hp.

 

[lwarden]

Over on boatdiesel one of the subscribers blew out the waterpump seal when pressuring with freshwater with the through hull ball valve closed and engine not running. Probably no reason to ever flush with the through hull closed as the fresh water flow will offset most if not all incoming raw water - at least at idle for anything under 1000 hp.

I found that my engines pull about twice what the hose can supply so I close the through hull when flushing. And yes, you need a way to ensure the line pressure is bled off to avoid blowing out a pump seal. In my setup that's what the check valve is for.

 

[firehoser75]

As with just about everything boat related, there are differing engine and exhaust setups, plus other idiosyncrasies from one boat to another. So, some boats can be safely freshwater flushed with the engine off (in these cases the FW usually enters the system "past" the pump), but for many/most, it must be running at idle to accomplish FW flushing safely (meaning no damage).

Especially for those whose setup requires the engine running, there is also a sequence or steps that must be followed to avoid putting pressurized water into your raw water cooling system with the engine OFF, which if not done correctly could cause problems. Many things in life require following steps in order. It is not "rocket science", and is easy to do, but it does require paying attention to what you are doing. The steps/instructions used have been put into several responses to FW flushing questions on this forum.

The main point when your setup requires the engine running scenario is to not allow pressurized water to have "access" to your engine when it is not running AND the through hull is closed at the same time. Yes you can still FW flush (not as effectively) with the thru hull open or even partially open with the engine running.

Don't just trust me, go over to Tony Athens' site (Tony is a marine diesel expert) over at sbmar.com and look up all the free info there under Tony's Tips and the forums. If still unsure about anything, ask questions on the free forum and often even Tony will answer.

 

[Roustabout]

Here is where I buy mine: info@redzincs.com or 508-925-0399.

 

[DPKCK]

I flush by filling my bait tank with fresh water and then "drawing" the water from the bait tank through the engine with a hose connected to the seacock. Avoids any concern about pressurizing the system.

 

[Comodave]

You can also use a SeaFlush adapter to flush the engine. It draws water from a bucket so you don’t pressurize the engine with water.

 

[magna 6882]

as a follow up i was wondering if there are pros or cons to leaving the coolers empty. I was thinking i usually swap the zincs with my finger over the whole to hold the water in. Is there any benefit to letting the coolers drain when changing zincs then just leaving them dry for a couple months or do they need the water to prevent corrosion ?

 

[lwarden]

One additional benefit of setting up fresh water flushing is that when you do service on your raw water side such as changing out a zinc or impeller the water that comes out and runs all over the engine and engine room is fresh and therefore won't create corrosion. I would say if you flushed and then drained the heat exchanger or aftercooler you should be better off than if it contains water. Doubt it would make much difference over containing fresh water though.