Fresh water flush??

Hi all,

So I came from a walk around style Kencraft with an 225 Optimax outboard that I kept in a slip. After each trip I did a balancing act to put the hose and "ear-muffs" on and run the engine with fresh water. I would do this even if I was going out the next day, its what the previous owner told me he did, and I suppose it gave me a warm and fuzzy feeling regarding salt corrosion.

Moving up to our Roughwater 29 earlier this year and doing basic maintenance on the 80 hp Ford Lehman, including replacing the raw water pump, some hoses and oil coolers has me thinking about this.

I make it a point, when I get to to the boat, to open the seacock valve and then close it again after my trip. I do have room to put a t-valve and hook up the hose.

So I guess the big question is, how many of you do this?? With the exhaust "elbow" on this Lehman as a spot that can corrode from the inside out I'm sure freshwater is better for it, but is this overly cautious in reality. I know the pencil zincs protect the heat exchanger, but wanted some real world thoughts.

Thanks, Keith

I think that if you can easily set it up so that you can do the flush easily each time you use the boat, I think that it would be a good idea. Now, if it is too much of a pain you may not do it.

I would love to be able to do it on my boat. However, if it is too much work I know I won't do it. I also have a space problem. There is no good way to add a T between the raw water strainer and the intake. I do have the room to add a T between the thru-hull and the strainer. I don't want to add it to the top of the strainer because that would limit access around my engine.

So, if you can find a way to do it so it is easy, I say go for it. This will be one of my coming winter projects.

A fresh water flush will pretty much assure that you never have to replace any raw water contacting parts. It is a PITA to do however. It is much more important on a high output diesel with more heat exchangers and particularly an after cooler. So I do it on mine.


David

We always flush our generator with fresh water if it is going to sit for a week or more. The engine intake is 2" so it s not practical to flush it after each use. But we do flush it if the boat is going to sit for a month or more. Remember, it is not a good idea to just hook up a hose. if the engine is running, the water pump will move the water through the system and the engine exhaust will push it overboard. But if you flush the engine and it is not running you will fill the muffler and backflood the engine. I flush the generator by hooking it up to a 5 gallon water tank and run the tank dry and shut it off. To flush the engine, I open the close the seacock, open the sea strainer cap and run two water hoses simultaneously. While it is not enough cooling water to run the engine at high speed, at idle speed it is adequate water flow to protect the raw water pump impeller and flush the system. I shut the engine down and let the FW flow int the bilge too that helps keep the bilge sweet..

Have a tee after the strainer with a valve to a hose fitting with a old washer hose connected to the valve . When flushing I connect to a water hose , open sea cock,s tart engine ,open Valve and turn on city water. Then close seacock,let city water run for 3-5 minutes,turn off water then engine. This leaves city water in engines,cooler etc. Do this each month as I m at a slip in marathon and yes it is a pain,but I feel that fresh water is better than saltwater. Keeps the Lions at bay.

It would be interesting to see just what the effects were from flushing and how much fresh water is required to make a difference.

It would also be interesting to see what items are affected the most that flushing truly makes a difference versus just normal wear and tear.

Deckape, How big is your water intake hose? your system works fine so long as the engine is shut down simultaneously with the water. You know how to do it. Have seen several people try to flush their engine with this same system but the engine was not running. Being in Marathon, this is and excellent protocol to protect your engine.

I ran a boatyard that was a dealer for several engines including Yanmar and Cummins. We were a Mercruiser dealer too. One customer had a SeaRay 36. we set him up with a flushing system. The owner used his boat heavily. He was fastidious about flushing the engines . After 4 seasons we had to pull the heads for a valve job, the insides of the manifolds and risers still looked almost new! That convinced me to start flushing my own boat.

tadhana said:

Deckape, How big is your water intake hose? your system works fine so long as the engine is shut down simultaneously with the water. You know how to do it. Have seen several people try to flush their engine with this same system but the engine was not running. Being in Marathon, this is and excellent protocol to protect your engine.

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That's a great tip, and something I didn't think about. With the outboard I would shut the engine down and then turn the water off at a sometimes leisurely pace. They need to be shut down simultaneously with the possibility of water back flowing in through the exhaust.

The best setup is where only the engine pump draws water...no city pressure to feed the system. That way there can be no error in timing.

But if comfy with timing.....lots of ways to do it.

I still wonder that if the vast majority of fresh water cooled engine owners don't flush and it isn't a manufacturer insistence for warranty...and it isn't pushed hard by any outside influence....well...?

Good idea? Sounds it....but it sure isn't an overwhelming issue in anything but outboards.

I put Groco flush fittings on the four critical raw water supply lines on my boat (2 mains, 1 genset and one AC pump). I've heard people I respect say that they do and/or do not protect against corrosion. Do I know that they will help? Nope, but they make me feel better.

tadhana said:

Deckape, How big is your water intake hose? your system works fine so long as the engine is shut down simultaneously with the water. You know how to do it. Have seen several people try to flush their engine with this same system but the engine was not running. Being in Marathon, this is and excellent protocol to protect your engine.

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Every engine and every water supply is different. I won't know what procedure I will use until I actually start to do it.

Once I have the T in place I will first fill a 5 gallon bucket with water and have the engine draw water out of the bucket at the same time that I am filling the bucket with a dock hose. Get this all started with the engine running and the seacock open and then close the seacock and see if the dock hose can keep up with the engine demand at idle.

If the dock hose can put out more water than the engine demands, then it is easy. Open the seacock and start the engine. Open the valve on your flush system and turn on the dock hose. Any excess fresh water that the engine doesn't require will flow out the seacock.

If the dock hose can't keep up with the engine, then it is back to the 5 gallon bucket. Fill it up and keep the dock hose running into the bucket (in the aft cockpit) Start the engine, open the flush valve and close the seacock. Turn off the engine when the bucket is about to empty.

One of those two systems will work, but I don't know which one yet.

I have these Grocco fittings in my Air Conditioner intakes and generator intake. they make winterizing very easy. I do not generally use FW flush on the Air conds during the season . The air conditioner coils are a copper nickel alloy and are pretty resistant to corrosion. Thisis what I use to connect my generator intake to a 5 gallon tank for my weekly generator shut down flush.

Since I'm at the dock , once water is turned off ,five steps and I'm at the stop button to stop engine. I've had no problem with water flow ,at the exhaust as much water comes out with sea or city. Water is going to stay inside the coolers,maniflod etc. With sea water you have a salt that is corroding the areas as the water evaporates from the heat of the engine. This salt is what I want to flush out and leave just water in those areas. Weather it is good or a waste of my time,i don't know. But from my years of repairing marine engines and seeing what happens from not flushing ,I'll keep doing it and looking for positive results. Been flushing all my boats engines and with being at the dock for months at a time ,I believe that this is the correct thing to do.

Deckape said:

Water is going to stay inside the coolers,maniflod etc. With sea water you have a salt that is corroding the areas as the water evaporates from the heat of the engine. This salt is what I want to flush out and leave just water in those areas. .

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Thanks for all the replies.

Is 5,10,15 minutes or somewhere in between an adequate amount of time running the engine at idle with freshwater?

"A fresh water flush will pretty much assure that you never have to replace any raw water contacting parts."

Except the sea water pump rubber impeller.

These wear depending on the silt content of the water you cruse in.

ksandin, the fresh water flush merely is pushing the salt water out the exhaust. It only takes about a minute. two minutes is more than adequate. When the boat is running in salt water there is obviously salt water in the lines. When you start to add fresh water, it gets immediately diluted and is very quickly pushed through the system. It is the same amount of time that it takes to "pink" your engine at lay up. When you are winterizing, you run the engine, flush with fresh water and then start running the pink antifreeze through the cooling system. You run it until you have the pink solution out the exhaust. It takes only about 30 seconds to a minute.to get a good solid pink exhaust water.

At my dock I have a water meter ,so after 5-10 gallons,5 minute s or less I feel that all the salt water is out and I can stop the engine. When starting I let the engine get to temp ,check system s then start the flush. With my Perkins the combi cooler is the thing that I want to keep salt free.

With a little thought most fresh water flush systems could be used as an additional bilge pump in an emergency.

Most of these flush systems are set up for a 5/8 inch garden hose. I don't think a 5/8 hose could pass enough water Most sea water intake hoses are wire reinforced so that it won't collapse under suction. Do you think a 5/8 hose would stay open under suction?

At idle should not be a problem, even 1/2 inch hose keeps up with many smaller engines.

tadhana said:

Most of these flush systems are set up for a 5/8 inch garden hose. I don't think a 5/8 hose could pass enough water Most sea water intake hoses are wire reinforced so that it won't collapse under suction. Do you think a 5/8 hose would stay open under suction?

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I wouldn't use garden hose in a suction application but there are suction rated hoses available in 5/8".

Since most of these systems have female garden hose fittings to screw the hose into, you could go up to 3/4" hose for the suction hose.

Those that have the Groco Flush System pictured above mounted on the Seacock don't even need a hose. Just pull the plug out and shut the seacock once the water has risen above the flush fitting. This allows the system to move the maximum amount of water. As you point out, using 5/8" hose will reduce the water your engine pump could move.

The engine on my boat has an 1-1/4" seawater pump. I've installed a Tee and Ball Valve at the entrance to the strainer. I have an 1-1/4" pick up hose that leads down from the valve to the bilge. My plan is to open the valve and close the seacock if I have a flooding emergency my electric pumps can't stay ahead of.

After reading this thread, I'm going to give some thought to how I could use this as a fresh water flushing system. I guess I could just turn off the electric pumps, fill the bilge with fresh water and go from there. Actually that would be pretty easy.

I drilled and tapped the cover of my Perko strainer and attached a street el and fittings for a garden hose. See the pic below.

My Yanmar 6LY will suck a garden hose nearly flat with the seacock closed even at idle, but that is what I use and it works ok.

When I am finished flushing I close the fresh water supply and quickly shut down the engine.

David

Be careful about the metals. The street el and nipple are probably brass if you bought them at the hardware store. Unless you ordered them in bronze from a marine distributor, they are probably brass. You cannot tell by color alone. There are some brass castings that look like bronze. In my years running boatyards, I have seen brass fitting sink boats. Apollo makes valves in both brass and bronze. it is hard to tell them apart.

Another issue that I would never have thought was an issue. Here in Georgia Strait, I have never encountered anyone doing a fresh water flush on an inboard engine. Lots of folks with outboards do it, I even did it with an outdrive when I had one, but never on an inboard.
My first sailboat had a Ynamar YSE12, raw water cooled. I know I never flushed it in the 11 years I owned it. I ran across it when it was 30 yrs old and the then current owner had just repowered. Not due to lack of flushing. He was a Yanmar dealer's employee, so had good access to new engines, and told me he looked at the old one critically after he replaced it. His take on it was that it had gone 30 years and would likely go another 30.

I know there are other reasons to prefer to see fresh water in your heat exchangers, but paying attention to the rate of consumption of the zincs will address most of that. You still need to pay attention to zincs if you do adopt a flushing regime.

Just doesn't cry out to me as another thing I need to start doing.

Some engines have 7-8 zincs, and some have none. My Cummins has 3 zincs. Two in the aftercooler and one in the heat exchanger. There is no zinc in the fuel cooler or the transmission cooler. they are a very long distance from the engine zincs and could not be protected, so I prefer to flush if the engine is going to sit for a month or so in salt water. My Onan generator has no zincs, so it gets flushed if it is gong to sit for a week. Remember older engines such as your raw water cooled Yanmar are principally iron and steel. Modern engines have iron, steel, brass, bronze, aluminum and stainless steel. To me it makes sense to flush the salt out if it is going to sit. As an aside, here on the Chesapeake the water is brackish and engine zincs last 200 hours. In Florida they only last 100 hours.

Greetings,
Interesting that the subject of zincs came up. IF you flush with fresh water, won't your zincs develop an inert oxide coating as a result of sitting in fresh water thus rendering them useless?

No they do not seem to develop an oxide coating that renders them useless; they continue to function. I do use aluminum anodes on the hull becasue I spend a fair amount of the year in brackish to fresh water.

zincs really have nothing to do with fresh water flush or not. Anodes protect against galvanic corrosion which is different than aqueous corrosion.

The primary issue is for those of us with aftercoolers and heat exchangers. In a salt water environment, many manufacturers recommend a service every two years. Most of the time this doesn't get done. It can be expensive to have done unless you do the work yourself. If a core rust out, then they are very expensive to replace. Regular fresh water flushing helps reduce the service interval and the risk of rust. It is much better to have these items sit in fresh water than sit in salt water.

How much better is something that I don't know. Most of the time we only get to hear anecdotal reports of folks who have or have not used fresh water flush. My take is that if it can be setup relatively inexpensively and in such as way as to make it relatively quick and easy, then it is good idea. How easily, and how inexpensively depend largely on the boat however.

RT Firefly said:

Greetings,
Interesting that the subject of zincs came up. IF you flush with fresh water, won't your zincs develop an inert oxide coating as a result of sitting in fresh water thus rendering them useless?

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This is something that I have wondered myself. As far as I have been able to find out, the zincs do continue to function. However, I have considered switching to aluminum anodes in my heat exchanger and aftercooler if I come up with a fresh water system. Their would be no concern then with passivization of a zinc anode while sitting in fresh water.