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Old 07-02-2022, 07:27 PM   #1
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Do Any of You Freshwater Flush Your Engine?

On a regular basis that is?

As mainly a salt water day boater for the last 2 decades, I've been in the habit of flushing an engine, even if it was only run 5 minutes.
With the Mainship, I was concerned about not easily being able to do that. I've read a bit about cleaning heat exchangers and using barnacle buster. Worry about exhaust manifolds/elbow too.
I went ahead and plumbed in garden hose flush points for the Cummins and the generator. I have run both strictly on the flush with the seacocks closed, as well as with the seacocks open. No problems either way.

Not sure if practical to do when cruising, but feel it's like brushing and flossing.

Interested in opinions and experience of members.

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Old 07-02-2022, 07:33 PM   #2
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Does taking the boat to the Great Lakes every summer count as freshwater flushing?

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Old 07-02-2022, 07:35 PM   #3
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@ Skiff Builder,


To be honest I have not done it, but it does make sense to do it at the end of the season, in fact it makes a lot of sense. I always do it with outboard engines after each outing at sea, but for my Lehmans it would be a good idea.
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Old 07-02-2022, 08:49 PM   #4
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Every time,well 95 % of the time,unless I tie the boat up after midnight and have been drinking all day
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Old 07-03-2022, 06:00 PM   #5
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Yes, I have installed fresh water flush systems on all my previous boats as well as my current boat and not only have I NOT had to do any heat exchanger work, but it saves the engine zincs too:-)
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Old 07-03-2022, 06:36 PM   #6
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Skiff B.,
I have freshwater flushed my Nordic Tug regularly from when I first bought her. Not every single run, but at least 80-90% of the time we are at a dock where freshwater at a decent flow is available. There is no doubt in my mind that it is effective, and is well worth the small effort required. A FW flush is especially important if the engine is going to sit unused for a while. We had connections for a dock hose on the raw water strainer lid of both the Cummins engine and the Gen Set. This made the procedure simple, easy, and not very time consuming. Tony Athens, a marine diesel expert swears by freshwater flushing and explains it well in several posts and articles on his website sbmar.com.
However, it might be worlth switching to aluminum anodes in your engines instead of zinc if you either freshwater flush or regularly go back and forth between salt and freshwater. Freshwater exposure causes a "coating" to form on zinc, reducing (or even eliminating) it's effectiveness as an anode (without manually removing the coating). That is why people say "freshwater flushing saves zincs"! If they are not eroding, then they are probably not protecting other engine metals as well as they could be.
FW flushing reduces "marine aging" of your engine(s). This "marine aging" occurs whether your engines are being used or even just sitting full of saltwater.
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Old 07-03-2022, 07:14 PM   #7
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Freshwater flush

Quote:
Originally Posted by Skiff Builder View Post
On a regular basis that is?

As mainly a salt water day boater for the last 2 decades, I've been in the habit of flushing an engine, even if it was only run 5 minutes.
With the Mainship, I was concerned about not easily being able to do that. I've read a bit about cleaning heat exchangers and using barnacle buster. Worry about exhaust manifolds/elbow too.
I went ahead and plumbed in garden hose flush points for the Cummins and the generator. I have run both strictly on the flush with the seacocks closed, as well as with the seacocks open. No problems either way.

Not sure if practical to do when cruising, but feel it's like brushing and flossing.

Interested in opinions and experience of members.

Thks, Skiff Builder
I installed a freshwater flush system on the single Cummins 6BT 5.9-M engine that powers our trawler after purchase. I flush with fresh water for 5 minutes at idle with the seawater thru hull valve closed after every cruise except when freshwater is not available. I place the freshwater flush intake hose in a 5 gallon bucket to flush while running the dock hose fast enough to keep the bucket full. Since the water in our marina is brackish, all of the anodes were switched to aluminum including the HX anode when we moved to this marina. The HX anode on my engine is not bathed in water when the engine is off. I believe the fresh water flush is worth the little time and effort it takes to complete the flush.
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Old 07-03-2022, 08:01 PM   #8
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I have not had to flush any of my engines throughout my boating career of 35 years however, my home ports were always in brackish waters areas (Northeast in upper Chesapeake MD and almost Tarr river on the Pamlico river NC). I do go to saltier waters but it usually gone by the time I get home to my brackish waters. Also all my engines were antifreeze cooled w/heat exchangers.
Good luck,
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Old 07-04-2022, 03:27 PM   #9
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I do not flush the engine (Yanmar 4JH2) on my boat. I kind of feel that the risk of water backing up into the cylinders negates any benefit from flushing. I've only owned the boat a few years and don't know what previous owners did, but I opened up the heat exchanger on this 20 year old engine recently and did not find any corrosion or blockage.
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Old 07-04-2022, 05:02 PM   #10
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Originally Posted by ScottRhodes13 View Post
I do not flush the engine (Yanmar 4JH2) on my boat. I kind of feel that the risk of water backing up into the cylinders negates any benefit from flushing. I've only owned the boat a few years and don't know what previous owners did, but I opened up the heat exchanger on this 20 year old engine recently and did not find any corrosion or blockage.
If the fresh water is introduced into the cooling system before the water pump, technically it wouldnít be anymore of a risk than normal raw water flowing through the same system.
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Old 07-05-2022, 01:07 PM   #11
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Scott,
Southern Boater has it right. If the freshwater is introduced at the sea strainer with the engine running, all you have done is either mix fresh with saltwater (if sea cock is open) which is still good, or replace the saltwater with fresh (if the sea cock is closed)! However, do not introduce pressurized freshwater from the dock with the sea cock closed and the engine off! That could create a problem. However, running pressurized freshwater into the strainer with the sea cock open (and the engine off) is not a problem as the pressure just exits the boat underwater through the open sea cock.
There is more to a "healthy" cooling system than no corrosion or actual blockages!
All raw water cooling system components should be periodically taken off the engine and completely serviced, which includes: cleaning, inspection, replacing seals and/or O rings, and PRESSURE TESTING. These components, even with proper maintenance, do have an expected "service life", and the only way to know they are still functioning (properly) is with a complete service (otherwise you are actually guessing). You don't want an internal leak to allow saltwater into the various lubricants, or engine coolant, or maybe into the air intake for combustion (if you have an aftercooler).
Take the time (my suggestion) to investigate freshwater flushing by going to sbmar.com under Tony's Tips (and/or under his forums). The info is from a marine diesel expert with over 35 years experience servicing these engines (and is competely FREE). I found the evidence to be compelling. JMHO.
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Old 07-05-2022, 08:09 PM   #12
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I have not done this but like the idea.
Since raw water travels through when engine runs, what if the fresh water inlet is plumbed after the impeller so the engine does not need to be running?
What about the riser does it expel raw water in a way not to flood the engine if not running. Guess that is the reason engine should be running.
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Old 07-05-2022, 09:06 PM   #13
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I have not done this but like the idea.
Since raw water travels through when engine runs, what if the fresh water inlet is plumbed after the impeller so the engine does not need to be running?
What about the riser does it expel raw water in a way not to flood the engine if not running. Guess that is the reason engine should be running.
It depends on the exhaust geometry. Some would be ok, some would flood the engine. Safest option is to let the impeller draw water and flush with the engine running.
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Old 07-06-2022, 12:49 AM   #14
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Originally Posted by DLETF View Post
I installed a freshwater flush system on the single Cummins 6BT 5.9-M engine that powers our trawler after purchase. I flush with fresh water for 5 minutes at idle with the seawater thru hull valve closed after every cruise except when freshwater is not available. I place the freshwater flush intake hose in a 5 gallon bucket to flush while running the dock hose fast enough to keep the bucket full. Since the water in our marina is brackish, all of the anodes were switched to aluminum including the HX anode when we moved to this marina. The HX anode on my engine is not bathed in water when the engine is off. I believe the fresh water flush is worth the little time and effort it takes to complete the flush.
I like your MO. Sounds failsafe for not flooding the incorrect motor parts; simple to utilize too. Having just reentered saltwater after 14 yrs in freshwater... I may copy your method.
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Old 07-06-2022, 01:15 AM   #15
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On our last boat we used a SeaFlush adapter to winterize the engine. It work just as well for freshwater flush of the engine. You take cap off strainer and remove the basket. Put the SeaFlush adapter into the strainer and suck freshwater in from a 5 gallon bucket. Simple and easy. No problem since you run the engine to suck in the freshwater.
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Old 07-06-2022, 09:47 AM   #16
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On our last boat we used a SeaFlush adapter to winterize the engine. It work just as well for freshwater flush of the engine. You take cap off strainer and remove the basket. Put the SeaFlush adapter into the strainer and suck freshwater in from a 5 gallon bucket. Simple and easy. No problem since you run the engine to suck in the freshwater.
Thatís great, and avoids the potential problems of too much water pressure being pushed into your cooling system but also the opposite: If pump suction exceeds the hose pressure it can suck the hose flat and create havoc pretty quickly (wrecked impeller and overheating).

I put in a bronze tee between my seacock and strainer that goes to a valve that draws from my water tank. (I plumbed the hose to a rigid pvc intake that drops thru the top of the tank thru a bulkhead fitting in a plate and can be removed for use as a crash pump). The largest bronze tee I could find was 11/4Ē so this might be limiting if you need a larger size. The valve is located above the outside water line and will not see seawater so brass is OK. One of the advantages is I can see how quickly the engine draws water from my plastic tank and quickly determine the output of my pump and impeller performance.
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Old 07-06-2022, 10:35 AM   #17
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I keep my boat in salt water and fresh water flush when I leave it long term.

I read in other threads here that zinc anodes in fresh water is not such a great idea.

So my question is does a fresh flush sitting all winter render heat exchanger zinc anodes ineffective?
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Old 07-06-2022, 10:36 AM   #18
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It certainly could. I would switch to aluminum anodes if you do freshwater flushes.
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Old 07-06-2022, 10:47 AM   #19
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My first sailboat was new in 1977. A Yanmar YSE12, single cylinder, raw water cooling, for power. I ran across it again after 30 years, and was told by that owner that he, being a Yanmar retailer, for no reason other than that he got a super deal on a new Yanmar, it was re-powered. He then tore down the original engine and reported no build up of salt, no internal signs of age at all. I know that in my ownership of 11 years, it had never been fresh water flushed, never stored in fresh or brackish water. He confirmed the same for the next 20 years.
YMMV
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Old 07-06-2022, 11:39 AM   #20
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Is there much risk of metal damage when the heat exchanger sits in Fresh Water? Obviously, salt water causes much more corrosion but what about metals in fresh water? I've never seen any issues by leaving Zinc's in my system after a fresh water flush.....I'm not going to go through all the hassle of changing all the zincs to aluminum, then changing back to Zinc when I am in salt water. That is too much work for me..... Since fresh water flushing and staying with Zinc has worked fine for all of my previous boats, I'm going to stick with that process. I wonder if Steve D can chime in on this subject?
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