Fresh Water Flush

[dhays]

Zincs lasted several times longer.

Another good point. I switch to aluminum pencil anodes when i started doing a fresh water flush. That way my anodes are still effective when the boat is sitting with fresh water in the engine cooling system.

 

[lwarden]

Freshwater flushing was popularized by Tony Athens, first on boatdiesel and later on his own web forum at Sbmar.com.

One of the reasons is that the Cumins engine, which Tony promotes (not unreasonably) has a vulnerable sea water after cooler that needs regular maintenance attention. Fresh water flushing extends that maintenance interval according to Tony.

My Yanmar 6LY went ten years before I bought it and serviced the after cooler and it wasn't too bad. I think a Cummins after cooler would have been toast after ten years without freshwater flushing.

YMMV.

David

I have the Cummins engines so this is the reason I flush the engines. My aftercoolers are due for servicing so looking to keep the salt in them to a minimum until I do a tear-down in January and rebuild them. Even after, seems better for all internal components including the water pump to have it sit with fresh (or mostly fresh) water in it. Call me OCD, I don't mind

 

[dhays]

I have the Cummins engines so this is the reason I flush the engines. My aftercoolers are due for servicing so looking to keep the salt in them to a minimum until I do a tear-down in January and rebuild them. Even after, seems better for all internal components including the water pump to have it sit with fresh (or mostly fresh) water in it. Call me OCD, I don't mind

Yup. I have the Cummins as well. If I didn’t I may not have decided to do the flush.

 

[Hornloaded]

I have been flushing for the last 1-1/2years every time I start the engines. I just pulled my zincs for the first time and had a look. Zincs are still the original size and the After Cooler looks new inside. I also have Cummins and did everything Tony Athens suggested.

 

[Greggnvt]

My previous boat was a Gas Volvo I/O - which I did run in saltwater as the boat was docked in saltwater - pulled out annually. The engines (basically Chevy's) were easy to get to and I rigged up a freshwater rinse that I did after EVERY run, mostly for the benefits of the exhaust risers - the poor out-drives were on their own (but did very well - kept up with the anodes).

My current boat has been in saltwater for 30 years (Cat 3208TA's) until June of this year - I've never done a freshwater flushing of the engines - although, I swear I heard an "Ahh" out of the exhaust when we dropped down from the last lock to the cool freshwater of Lake Champlain!

Gregg

 

[La Sirena]

You flush the seawater out with freshwater from the dock every time you return from a run? On first blush and not being in salt water (yet), that seems like a lot. The more I think about it however, the smarter it sounds. Does everyone in salt water routinely flush their engine(s) with freshwater?

I don't do a freshwater flush EVERY time I use the boat, but I do if the boat will be sitting for a week or more. I do freshwater flush on all 4 engines (main, wing, generator and dinghy outboard) plus the A/C circulation loop. Tony Athens, Cummins and diesel expert, highly recommends doing so, so that is what I do. If I was running a commercial operation and the boat was run daily, I wouldn't do a freshwater flush.

Here's why (expanding on what a couple other people said). Diesel engine aftercoolers are cooled either by coolant or by seawater. Cummins and many other manufacturers cool aftercoolers with seawater. There is only one large seal (o-ring) between the seawater and engine air intake in the aftercooler. If that seal leaks you get seawater ingested into your engine's combustion chambers. Not good. Seawater, particularly if it remains stagnent for a long time, could erode the cast iron seal seat and create a path for the seawater to enter the combustion chamber. By flushing the seawater out, it will dramatically slow the corrosion process of the aftercooler seal's seat. Even so, it's recommended to remove the aftercooler and replace the seal every 2 years, regardless of the number of hours you put on the engine.

 

[firehoser75]

I strongly agree with those who follow Tony Athens' advice regarding the usefulness of regular freshwater flushing. Go to his website (sbmar.com) and check it out for yourself!!! He has tons of free info under Tony's Tips or on his several forums (just search the forums), complete with photos involving his many, many years of experience showing the positive results (and the negatives of not flushing and neglect) of freshwater flushing. It literally took me 10-15 minutes from getting the hose out of the laz to putting it back to complete a freshwater flush of both engine and generator. It is simple, safe, and greatly reduces the possibilities of engine overheats caused by the raw water system and can increase the time interval between full (off engine) servicing of the raw water system components.

However, even with freshwater flushing, or using Barnacle Buster (or other), you still need to take the various components off the engine for full servicing. Why you may ask? EG. the aftercooler. Most aftercoolers consist of several components made from different metals, that are at different levels on the corrosion scale (anode to cathode). Put different metals in an electrolyte (saltwater is a very good electrolyte) and you create a type of battery where one metal will give up electrons and "sacrifice" itself. This corrosion often occurs at the interface where the sealing "O" ring sits, possibly resulting in saltwater leaking into the combustion chambers (not good), and/or basically welding the 2 metal pieces together resulting in the need for a complete new aftercooler (not cheap). Another reason they need to be disassembled and properly cleaned, is the air side of the aftercooler. No amount of BB or freshwater flushing is going to affect the air side at all!!! Oily gunk (from most CCV systems) will build up on the air side, slowly starting to "air starve" the engine resulting in poor performance and other issues. This can only be avoided by disassembly and a proper cleaning. Once cleaned up, greased up to slow down future corrosion, and reassembled, the unit MUST be pressure tested. There is no other way to know for sure that you are not adding some saltwater to your engine's intake!!
The other components have similar (but not as bad or as many) issues. For example, the only way to ensure we don't have saltwater where we don't want it is by pressure testing as part of a full service.

Freshwater flushing can extend the time between this needed full servicing, and it is easy, and only takes a few minutes time, usually right after docking and the boat is secured.

A regular garden hose (best if the hose is relatively stiff to minimize collapsing) is all that is needed as long as the dock water has a reasonable volume (flow rate). I had the hose attachment on the sea strainer making it very easy.

 

[Lucie]

I am interested in this idea. I was thinking of plumbing a fresh water flush from the onboard water tanks. No dragging hoses through the boat. I thought it could be cut in before the electric water pump so the water is drawn from the tanks via the raw water pump. My only concern is the size of the current water line from the tank being too small but I wonder if this is a problem just at idle.
Andrew

 

[firehoser75]

I am interested in this idea. I was thinking of plumbing a fresh water flush from the onboard water tanks. No dragging hoses through the boat. I thought it could be cut in before the electric water pump so the water is drawn from the tanks via the raw water pump. My only concern is the size of the current water line from the tank being too small but I wonder if this is a problem just at idle.
Andrew

Andrew,
I don't know why you would need to try to do it this way and use (valuable due to limited capacity) tank water instead of taking the very few minutes to get out a hose?? The engine could use up to 10 gal. per minute at idle so even a short 3 minute flush would need around 20-30 gallons of tank water? (say 1/4 to 1/3 of a tank on a lot of boats).

Just connect a "stiff" dock hose to a "garden hose" fitting on your sea strainer. Open thru hull and turn on dock water (pressure exits the bottom of the boat and actually backflushes the thru hull). Start engine and close thru hull (could leave thru hull fully or partially open and still receive benefit). Run for 3-5 minutes at idle. Shut down dock water and engine at same time, or water first followed by engine in a few seconds. Open thru hull to relieve any pressure (and if you normally leave it open). Put hose away. If you are worried about your impeller (there should be no problem as long as dock water has reasonable flow), put your hand on the raw water pump cover. If it is not hot, you have enough flow! If it feels very warm to hot, just open thru hull (partially or fully as needed). You only need enough water to keep the impeller cool when running for only a few minutes at idle.

As a boater, do you NEED to freshwater flush. Absolutely not. Many, many boaters do not, but, they miss out on the benefits. However, experience has shown that there are many benefits to doing a freshwater flush regularly (doesn't have to be after every run). However, proper preventative maintenance is still required (just less often and the system is kept in better overall condition between services) to keep your engine's cooling system operating at peak efficiency. Overheats can be VERY damaging to engines. Aftercoolers are a special item, and require servicing more often than the other components (should service every 2-3 years, with FW flushing can probably extend that time to every 3-4 years). An important part of all full servicing of the raw water cooling system components is PRESSURE TESTING. Without pressure testing, you could have sea water leaking into your transmission, or into your coolant, into the fuel supply (leaking fuel cooler), into the engine's air intake, etc.
Paying for a full service of your raw water cooling system can run several thousand dollars (depending on mechanic rates), so extending the time between services can be worth it monetarily, to say nothing about the peace of mind knowing your system is well maintained. I did my own servicing, but it is time consuming and reducing that by spending 10 minutes to regularly FW flush makes sense to me.

 

[Njlarry]

I have long wondered if flushing is of much help on fresh water cooled genny as the raw water side is very short, mostly just affecting the heat exchanger. But the main engines with aftercooler and other coolers is different.
What I dont understand is the concern about city water pressure. I am neither a plumber or an engineer but will 60 lbs in a small garden hose get reduced going into a much lager cooling system??

 

[JPMyers]

I was thinking of running a permanent water line to a manifold in the ER. From there I could select engine, generator, or AC cooling intake. Which brings we to the question, is it Okay to great flush the AC system?
I would leave the sea cocks open to act as a pressure regulator.

 

[DavidM]

I have long wondered if flushing is of much help on fresh water cooled genny as the raw water side is very short, mostly just affecting the heat exchanger. But the main engines with aftercooler and other coolers is different.
What I dont understand is the concern about city water pressure. I am neither a plumber or an engineer but will 60 lbs in a small garden hose get reduced going into a much lager cooling system??

I think the main beneficiary of fresh water flushing is the aluminum shell to bronze tube sheet o ring seal on turbo charged and after cooled engines. For a NA engine like your generator, the metals in contact with sea water are all cupronickle or bronze, both highly resistant to sea water corrosion. So fresh water flushing less helpful there.

With regard to city water pressure, the main concern is blowing the raw water pump seal if you put that much pressure on it. This will happen if you hook up water to the strainer with the seacock closed and the engine not running. 60 psi is definitely enough to blow the seal on a pump that usually operates at or near a vacuum on the suction side.

With the engine running, the sea water pump usually pulls more gpm than the hose can deliver (at least that is how it worked with my dock water supply) so the pressure at the pump is very low and there is little risk of blowing the pump seals.

But 60 psi is a lot more than my dock water supply was so I would be careful. Maybe put an RV type pressure regulator on the hose.

David

 

[DavidM]

I was thinking of running a permanent water line to a manifold in the ER. From there I could select engine, generator, or AC cooling intake. Which brings we to the question, is it Okay to great flush the AC system?
I would leave the sea cocks open to act as a pressure regulator.

With the sea cock open you are not going to build up any pressure on the water supply so the engine's raw water pumps should work fine. But unlike raw water pumps on engines, the March and Cal pumps used on A/C systems are not self priming, so you may not get any water flow without burping them. In any case I wouldn't worry about flushing the A/C system. It is all cupronickle and rubber tubing which won't corrode much. Scale buildup during operation is the bigger problem with marine A/Cs.

David

 

[rslifkin]

As an interesting note on scale buildup, some of the stuff that accumulates in heat exchangers, etc. will dissolve in fresh water. When I first brought my boat into fresh water, after the first overnight sitting with fresh water in the heat exchangers and such, it blew a whole bunch of junk out the exhausts on startup the next morning. And after a couple of days of running in fresh water, my coolant temps up on plane were 3 - 5 degrees lower, so some buildup in the cooling systems must have dissolved.

 

[Njlarry]

Thank you Dave, understood.
Tom do you have a parts list for the groco strainer you show?
Great discussion, thank you all.

 

[firehoser75]

Thank you Dave, understood.
Tom do you have a parts list for the groco strainer you show?
Great discussion, thank you all.

Yes, I have a Groco parts list, but I am not sure that they (OEM) sell the lid with hose bib. Seaboard Marine (in California) does, but you will need to know your model number. I have no affiliation with Seaboard, only believe in supporting Tony especially due to the loads and loads of excellent, free advice he gives on his site (sbmar.com).
If you want a copy of what I do have, send me a PM with your email address and I will attach a copy.
Merry Christmas everyone,
Tom

 

[Lucie]

Hi Tom,


Thanks for your input. I totally agree that it a good idea and as I am the chap that does the servicing, anything that will extend the life of the raw water system has to be a good thing. My thoughts of connecting to the onboard tanks was purely for convenience. I almost always top up our water tanks prior to leaving the dock, so the water is not all that valuable at the end of our trips. However I do take your point. I'm not sure the outlets from the water tanks would allow enough flow anyway so a variation on your idea might work for me by running a hose to the stern which could be connected externally.
cheers Andrew

Andrew,
I don't know why you would need to try to do it this way and use (valuable due to limited capacity) tank water instead of taking the very few minutes to get out a hose?? The engine could use up to 10 gal. per minute at idle so even a short 3 minute flush would need around 20-30 gallons of tank water? (say 1/4 to 1/3 of a tank on a lot of boats).

Just connect a "stiff" dock hose to a "garden hose" fitting on your sea strainer. Open thru hull and turn on dock water (pressure exits the bottom of the boat and actually backflushes the thru hull). Start engine and close thru hull (could leave thru hull fully or partially open and still receive benefit). Run for 3-5 minutes at idle. Shut down dock water and engine at same time, or water first followed by engine in a few seconds. Open thru hull to relieve any pressure (and if you normally leave it open). Put hose away. If you are worried about your impeller (there should be no problem as long as dock water has reasonable flow), put your hand on the raw water pump cover. If it is not hot, you have enough flow! If it feels very warm to hot, just open thru hull (partially or fully as needed). You only need enough water to keep the impeller cool when running for only a few minutes at idle.

As a boater, do you NEED to freshwater flush. Absolutely not. Many, many boaters do not, but, they miss out on the benefits. However, experience has shown that there are many benefits to doing a freshwater flush regularly (doesn't have to be after every run). However, proper preventative maintenance is still required (just less often and the system is kept in better overall condition between services) to keep your engine's cooling system operating at peak efficiency. Overheats can be VERY damaging to engines. Aftercoolers are a special item, and require servicing more often than the other components (should service every 2-3 years, with FW flushing can probably extend that time to every 3-4 years). An important part of all full servicing of the raw water cooling system components is PRESSURE TESTING. Without pressure testing, you could have sea water leaking into your transmission, or into your coolant, into the fuel supply (leaking fuel cooler), into the engine's air intake, etc.
Paying for a full service of your raw water cooling system can run several thousand dollars (depending on mechanic rates), so extending the time between services can be worth it monetarily, to say nothing about the peace of mind knowing your system is well maintained. I did my own servicing, but it is time consuming and reducing that by spending 10 minutes to regularly FW flush makes sense to me.

 

[Bob Nala]

Inline T with ball valve right after the strainer. $100cdn. This was a BB flush. next connect waterline from FW tank to ball valve, just a quick rinse if she is going to sit for a week or two. Managed to remove a lot of crap from the RWC.

 

[Lucie]

Inline T with ball valve right after the strainer. $100cdn. This was a BB flush. next connect waterline from FW tank to ball valve, just a quick rinse if she is going to sit for a week or two. Managed to remove a lot of crap from the RWC.

Well done. I like it.
It would extend the service interval of the RWC by a long way.

 

[Hookmeup]

Intercooler bypass Cat 3208

I run my TA Cats at about 1400 rpm below turbo kick in. In fact I cruise on 1 engine in a 44 foot Symbol for 7-8 knots. I have just bypassed my aftercoolers due to the risk of seawater to the intake. I added a mount and simply rotated the hose 90's and added a short coupling. If I ever need to reconnect its a five minute job I'll see on the next cruise if I need that added 50 hp to get up on a plane to run 18-20 knots if I needed it in an emergency. I expect it may run rich at 2400 rpm as the combustion air mass will be low.

 

[lwarden]

Thought I'd post the mess I found when servicing my aftercooler. Although they were done in 2017 the boat sat for months by the PO without flushing. One of the cores required replacement and the other cleaned up. I will be on a 3 year schedule and will flush after every use if we are away from the boat for more than a few days. These Cummins aftercoolers are not the best design IMO but proper maintenance, and service per Tony Athen's procedure and flushing should give these a long life. With as blocked as the one core was it's amazing the boat reached close to WOT.

 

[DDW]

The blockage in the tubes wouldn't affect WOT, that's just the cooling water. Might affect EGT though.

For contrast, here is my aftercooler core, first look after 13 years of operation with fresh water flush anytime it was not used for more than a few days. Only about 4 of those years in salt water though.

 

[lwarden]

The blockage in the tubes wouldn't affect WOT, that's just the cooling water. Might affect EGT though.

For contrast, here is my aftercooler core, first look after 13 years of operation with fresh water flush anytime it was not used for more than a few days. Only about 4 of those years in salt water though.

View attachment 125864

Not so sure about that DDW. Lack of cooling of air input to the intake from the turbo could affect overall HP and therefore top end. At least that's what I understand the purpose of the AC is.
BTW, I presume you resurfaced the o-ring surface on that housing as it looks like a potential for leaks. Both my housings had that issue and were resurfaced, painted with zinc phosphate and epoxy before reassembly.

 

[Snapdragon III]

I have flushed my engines by just closing the sea cocks, taking the tops off the strainers, and letting the hose run into them and overflow into the bilge, then start and run the engine. It worked pretty good, but was a pain. The only time I have done it was when I knew the boat was going to sit for months unused in Hawaii, and when I was going to change pencil zincs, or change pump impellers. I figure it is worth the hassle for any job where I will likely spill water all over, much less chance of making a rusty mess if it is just fresh water. I have old school naturally aspirated engines, so no after coolers to worry about.

 

[Reef Wanderer]

My simple solution for fresh water flush on my Ford Lehman 120hp, was too place a tee piece in the sea strainer to raw water pump hose. Then a 20 liter plastic jerry can positioned way forward in an empty area of the engine room against the forward bulkhead. I fitted a 1&1/2" male pipe fitting in the lowest area of the side of the jerry can and then a hose connecting into the Tee piece after the sea strainer. Plus a full flow valve inline. I fitted a line from the boat freshwater supply into the top of the jerry can.
Just after returning home from sea, we turn on the fresh water supply tap to the jerry can and watch till it's full. Turn off the sea cock to the sea strainer (standard practice anyway). Turn on the inline fresh water valve from the jerry can. Start motor and monitor the consumption through the translucent jerry can. When fresh water level reaches the top of flush hose, turn off the motor and close the inline valve. In my set-up the 20 liter fresh water flush lasts around 40 seconds. The jerry can sits comfortably without any support (the hose holds it against the bulkhead, plus it is empty when underway. It has been in use for two years right now (260 hours) and after just pulling the raw water impeller to change, I looked at the oil cooler and main heat exchanger cores and they were perfectly clean and clear of any salt/calcium build-up. We operate only in sea water (no fresh water in Western Australia). Couple of photos below.

 

[Taras]

I have the same set up as DavidM (picture above). I have been installing fresh water flush systems in all the boats I've owned over the last 20 years and have never had to do Heat Exchanger repairs (saves zincs too). I permanently plumb mine to the fresh water tank of the boat and flush each time the boat sits for an extended period. Note that I do not plumb the line "after" the fresh water "pump" of the boat. Instead, just plumb it directly to the tank WITHOUT using the boats fresh water pump. The impellors of the motor will pull the water out of your fresh water tank. No need for pressurized water to enter the sea strainer and potentially flood an engine with fresh water

 

[catalinajack]

My simple solution for fresh water flush on my Ford Lehman 120hp, was too place a tee piece in the sea strainer to raw water pump hose. Then a 20 liter plastic jerry can positioned way forward in an empty area of the engine room against the forward bulkhead. I fitted a 1&1/2" male pipe fitting in the lowest area of the side of the jerry can and then a hose connecting into the Tee piece after the sea strainer. Plus a full flow valve inline. I fitted a line from the boat freshwater supply into the top of the jerry can.

Just after returning home from sea, we turn on the fresh water supply tap to the jerry can and watch till it's full. Turn off the sea cock to the sea strainer (standard practice anyway). Turn on the inline fresh water valve from the jerry can. Start motor and monitor the consumption through the translucent jerry can. When fresh water level reaches the top of flush hose, turn off the motor and close the inline valve. In my set-up the 20 liter fresh water flush lasts around 40 seconds. The jerry can sits comfortably without any support (the hose holds it against the bulkhead, plus it is empty when underway. It has been in use for two years right now (260 hours) and after just pulling the raw water impeller to change, I looked at the oil cooler and main heat exchanger cores and they were perfectly clean and clear of any salt/calcium build-up. We operate only in sea water (no fresh water in Western Australia). Couple of photos below.

Wow, that is a ton of bother every time you start the engine. Sure, it preserves the exchanger. Not for me for my FL120s. Once a year, I close the seacocks, drain the exchangers, replace the drain plug, remove the anodes, fill the exchangers with a solution of phosphoric acid, and let the acid do its work. When I remove the end caps to inspect the only occlusion I find is bits of anode that have broken off. Way, way less work than fussing with fresh water flushes every time an engine is started. By the way, phosphoric acid is the active ingredient in Barnacle Buster and is inexpensive. One gallon makes at least 10 gallons of solution.

 

[Caballero II]

You flush the seawater out with freshwater from the dock every time you return from a run? On first blush and not being in salt water (yet), that seems like a lot. The more I think about it however, the smarter it sounds. Does everyone in salt water routinely flush their engine(s) with freshwater?

Well, I do. Except when we're in a hurry, and don't. Then, it's on our agenda and we come down to the marina and fresh water flush the engine within a day or two. We have placards to remind us that the seacocks are open or closed, so that's part of the process. Unlike, Tony's video, when we fresh water flush we leave the sea cocks closed, and post the placard. I get why he is doing that (leaving the seacocks open), but we don't do that and are looking to avoid the "sinking at the dock" scenario. So, seacocks are always closed when we are in our berth. Not a big deal. Only fresh water sits in our engine, unless we have been lazy and not flushed upon our return.