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Old 01-09-2017, 09:04 AM   #1
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The case for fresh water engine flushing

I plan to write an article for boatdiesel on this topic including plumbing systems to make it easy to flush, so I thought I would throw out some thoughts and get your comments before I start on it.

The case for flushing your engine's raw water system with fresh water after each use is that it reduces corrosion of the metal components. So let's examine why:

Without a doubt, the principle components in a raw water system, bronze end caps and cupro-nickle tubes, corrode less in fresh water than salt water. And some, Tony Athens in particular, recommend fresh water flushing to extend the life of after coolers which are susceptible to failure in a marine environment.

Let's examine the two premises.

Yes corrosion is less in fresh water, but what about the effect on protective anodes. ABYC and others recommend aluminum anodes in fresh water service because zinc forms a protective film in fresh water that makes it ineffective as a sacrificial anode. Aluminum anodes are effective in both fresh and salt water.

So, if we flush with fresh water and use zinc anodes aren't we losing the protection of the zinc when we run the engine in salt water? I have posted that fresh water flushing extends the life of my zincs several fold. Maybe I am just kidding myself. Perhaps the solution is to flush with fresh water and use aluminum anodes. You get the best of both worlds: low corrosion while sitting at the dock, but also protection while operating in sea water.

Now let's talk about after coolers. The problem with after coolers is that there is a tiny barrier between the air side and the salt water side- an o-ring that separates the two. The o-ring seals the bronze tube sheet of the heat exchanger bundle (core) to the aluminum shell.

But from looking at dozens of pictures of failed after coolers, they all have significant corrosion of the aluminum surface, not the bronze tube sheet. Fresh water flushing (with the proper anode) will reduce corrosion of the bronze, but not the aluminum. I believe that after coolers fail because condensate on the air side coupled with a salt air environment corrodes the aluminum to the point where the o-ring will no longer seal against it.

I don't know of any way to protect the aluminum other than to assemble the tube bundle to the shell with lots of water proof marine grease as Tony Athens recommends. The grease will keep moist salt air away from the critical o-ring interface.

So, here are my conclusions: Flush with fresh water but use aluminum anodes. Don't expect that flushing will extend the life of after coolers.

What are your thoughts?

David
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Old 01-09-2017, 10:16 AM   #2
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David,
There is a good argument that Aluminum anodes are a better anode for most any (non aluminum) boat and drive system (non aluminum). We changed from zinc to aluminum 3 years as we go. We go from salt to fresh and back to salt several times per year. Most of our year we are in brackish water. But I don't think anyone is making aluminum pencil anodes for engines. Let me know if you find a source. Cummins has told me that zinc engine anodes are fine even if you are using aluminum hull anodes. My own recent history confirms this. We change engine zincs about every 200 hours except when running the ICW and the boat is going every day and has some extended periods in FL salt water. Then we have to change the zincs every 100 hours. But over all, the engine anode life and change interval has not noticeably changed since we switched to aluminum hull anodes.

Cummins issued a service bulletin about 7 years ago to tell owners to remove, disassemble, clean and service the aftercooler once a year, rather than every two years as previously recommended. We have this service performed religiously every year. We run 600 hour per year. The corrosion is not so much affected by the hours of operation as it is affected by total hours of exposure to salt. Whether you run the engine 60 hours or 600 hours, over the course of a year the aluminum casting is exposed to salt for 8,760 hours.
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Old 01-09-2017, 10:22 AM   #3
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Dave- I have concluded that most of the aftercooler damage comes not from the seawater side, but from condensation on the air side. That is what rots the housings.
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Old 01-09-2017, 10:33 AM   #4
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"So, if we flush with fresh water and use zinc anodes aren't we losing the protection of the zinc when we run the engine in salt water?"


My main engines do not have zincs but with the outboards that I have flushed after use with saltaway and fresh water the zincs worked fine after the short rinses.


"Now let's talk about after coolers. The problem with after coolers is that there is a tiny barrier between the air side and the salt water side- an o-ring that separates the two"


Once again my main engines did not have this design or the associated issues you have described so far.
Perhaps the application would be more exact if it were "Fresh water flushing the Cummins 6b"
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Old 01-09-2017, 11:00 AM   #5
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The issue with the after cooler corrosion affects certain Cummins engines due to the aftercooler design. I believe there are other engines from other manufacturers that may have the same issue. In any event, the fresh water flush of a Cummins engine will not flush the air side of the aftercooler, so the problem exists and can not be washed away.
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Old 01-09-2017, 11:09 AM   #6
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David, this is a tie - in with a post you made recently on boatdiesel.com on engine flushing, with a picture of a strainer modified with fittings to take a dock hose. I have adopted this setup and it works fine. I have 6bts 210hp and no aftercoolers to worry about, but a fresh water flush is good for any marine engine.
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Old 01-09-2017, 11:28 AM   #7
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David,
There is a good argument that Aluminum anodes are a better anode for most any (non aluminum) boat and drive system (non aluminum). We changed from zinc to aluminum 3 years as we go. We go from salt to fresh and back to salt several times per year. Most of our year we are in brackish water. But I don't think anyone is making aluminum pencil anodes for engines. Let me know if you find a source. Cummins has told me that zinc engine anodes are fine even if you are using aluminum hull anodes. My own recent history confirms this.
#$%&, you are right. I just assumed that boatzincs would have aluminum pencil engine anodes. I just checked. They have magnesium ones, but strictly for fresh water use, not both. No aluminum anodes.

So I guess you flush and hope that your zinc anodes are still good for the few hours you run in salt water.

Ken:

When I write the article I will discuss the various commercial solutions for plumbing in a flushing system, but the home brewed system is by far the cheapest and works well.

smitty477 and others:

Cummins 6B and QSB engines have after coolers with a vertical bundle which lets condensate on the air side sit on the o-ring joint and corrode it out quickly. Yanmar engines have a horizontal bundle which lets condensate sit in the lower part of the shell so it is away from the o-ring joint for the most part. It does corrode though and after ten years in service my Yanmar 6LY was difficult to pull apart and had some light corrosion.

I am surprised that other after cooler designs don't use an o-ring or gasket at the water/air joint. I can't see how you could build them otherwise, but I have no personal experience other than Yanmar and Cummins.

Ski:

I have been recommending an extended after cooler service interval if you flush with fresh water. I am not going to do that any more.

David
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Old 01-09-2017, 11:34 AM   #8
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I have a Yanmar 4jh4-hte engine with turbo and after cooler. I've never serviced the after cooler or trans oil cooler because they are hard to get to. Are all those coolers really necessary if the engine is run at low RPM? Or were they mostly designed to let the engine run cooler at a higher RPM.

If a cooler fails can it be bypassed?
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Old 01-09-2017, 11:43 AM   #9
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Dave- I agree that the Cummins vertical core creates an inherent trap. Weak design. The horizontal cores like Yanmar do better, but cores still get stuck. It is not necessary for water to pool on the core/housing joint, just being damp sets up the cell just fine.

Any time I see aluminum housings with bronze end caps I cringe. Does not matter which fluid is being cooled, the housings tend to corrode.
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Old 01-09-2017, 11:46 AM   #10
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Performance Metals makes/sells aluminum pencil anodes. No more broken pieces lost in the cooling system.

Rudder Trim Tab Anodes
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Old 01-09-2017, 11:56 AM   #11
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I have a Yanmar 4jh4-hte engine with turbo and after cooler. I've never serviced the after cooler or trans oil cooler because they are hard to get to. Are all those coolers really necessary if the engine is run at low RPM? Or were they mostly designed to let the engine run cooler at a higher RPM.

If a cooler fails can it be bypassed?
The aftercooler cools the incoming air to improve the density before the turbo compresses it. If you do not service the after cooler according to the MFRs recommendation, the tube bundle may become so corroded in place that it cannot be removed. In that case you are going to replace the whole aftercooler. Probably cost 3-4 boat units. If the aftercooler O ring seal fails ( they fail due to corrosion), salt water can get into the incoming combustion air. AS you can imagine that is not a good situation at all. This will require a full engine rebuild. Might be possible to rebuild in the boat, but probably will require removing the engine. In 2010 I had a customer's aftercooler fail. Before anyone knee of the problem the cylinders were rusted and valves stuck. The rebuild cost 30-35 boat units back in 2010 (Cummins 8 cylinder). You cannot really take the aftercooler out and still run the engine. It is generally the first or second device in the salt water system. I guess you could bypass it with a piece of hose, but it is not a good idea. It is important to service it as often as recommended by the MFR!
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Old 01-09-2017, 12:07 PM   #12
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"I am surprised that other after cooler designs don't use an o-ring or gasket at the water/air joint. I can't see how you could build them otherwise, but I have no personal experience other than Yanmar and Cummins."


Hello David - here are some pics....


https://im1.shutterfly.com/media/47b...D550/ry%3D400/


https://im1.shutterfly.com/media/47b...D550/ry%3D400/
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Old 01-09-2017, 12:14 PM   #13
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Any time I see aluminum housings with bronze end caps I cringe. Does not matter which fluid is being cooled, the housings tend to corrode.
Ski - seldom mentioned but a big issue on after coolers is the terms and conditions under which an engine builder sub contracts them out. To keep it brief, they generally go to the low cost builder. Specifications, designs and drawings are let to the winning contractor.

Then the fun begins. Construction of a low volume after cooler may or may not be benched out with several other low volume non marine products. Welding rod, metal alloys and build specs cannot be easily verified by the engine guy except on paper. Side by side products destined for other non marine applications don't always require the same corrosion resistant rod or metal alloys. All they need to do is pass a pressure test.

Most after coolers will fail long after the warranty period has expired. Mine did. Over half the weldments were compromised. A 40 psi pressure test turned the cooler into a leaking nightmare. This was before it had ever been serviced. The problem lay squarely on the weldments from aforementioned third party build process.

Kind of ironic that Tony Athens recommends a tear down of a new Cummins after cooler to grease the sealing joints. Sure, it is a good idea but why should this be required at all on a new build?

And Cardude, yes one can bypass some after cooler designs. I was forced to do it when a cooler failed big time. Boating isn't always fun.
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Old 01-09-2017, 12:23 PM   #14
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The aftercooler cools the incoming air to improve the density before the turbo compresses it. R!
You may have this backwards for a few applications.
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Old 01-09-2017, 12:32 PM   #15
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Sunchaser, I suppose might, but I did run a Cummins and Yanmar marine engine service center.
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Old 01-09-2017, 12:44 PM   #16
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Aftercooler cools air after it exits turbo, not before. A high output marine engine runs at 30+psi of boost. Compressing that air raises temp to 400+F. Aftercooler takes it back down to 100F range.
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Old 01-09-2017, 12:47 PM   #17
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"Sunchaser, I suppose might, but I did run a Cummins and Yanmar marine engine service center."


I had a few Cummins in boats and one Yanmar in a larger inflatable and they all had intercoolers post turbo.
Which Cummins and Yanmar's engines have them prior to the turbo?
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Old 01-09-2017, 01:07 PM   #18
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Sunchaser

To be clear, I have been talking about aftercoolers. Not fuel coolers, oil coolers or trans coolers. What engine did you have where your aftercooler failed? You said it was long out of warranty, but did not say how old it was. Also, what was the brand name on the cooler? I think you will find that the big names in the marine cooler business are building their own coolers, and if not they have good incoming QC controls. Certainly things do fail, but usually there is a story behind the failure.

In my experience, your comments about subcontracted manufacturing does not matchup with my experience in the marine industry. I have serviced thousands of engines from all the big manufactureres in my career . My experience leads me to the conclusion that when the engines, coolers and engine zincs serviced according to the engine manufacturer's service schedule they will give many years of service.

We are coming up to 3k hours on our Cummins after 8 years of service. I asked Cummins if we should preemptively replace the coolers. They said there is no need to do that. I take this to mean that Cummins is tracking product failures and right now, cooler failures are not a significant risk for Cummins owners.

Tony is a real expert on Cummins. There is no doubt about that. I've talked to him several times. His recommendation is just that, his recommendation. It is not the recommendation of Cummins. In my years as a Cummins dealer we never had any trouble with coolers that were serviced on schedule. His comments do not mean that there is a problem out there. It is his recommendation. And certainly there is nothing wrong with doing it on a new engine.

Here is another odd thing about engines. After my engine was broken in I was going to run synthetic oil. I asked our Cummins service rep for my yard. He told me that was fine. But I still had to change the oil every 200 hours or void the warranty. He said that if I wanted to spend the money, well go on and spend it but Cummins did not see and advantage to it.
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Old 01-09-2017, 01:10 PM   #19
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Larry:

Thanks for the link to Performance Metals. I will buy some aluminum pencil anodes from them and install before next season.

smitty:

Your pics show a wider gasket sealing surface than are found on o-ring sealed after coolers, but it is still a bronze to aluminum joint that can corrode and fail.

sunchaser:

1. All engines with after coolers are installed after the turbo. There would be almost no point in running 90 degree intake air through an after cooler with 70 degree raw water to cool it maybe 10 degrees and then run it through the turbo. As Ski noted, after coolers cool the air hundreds of degrees because compression heats the air. So the AFTER cooler is after the turbo.

2. Tony Athen's shop disassembles and greases new after coolers because the factory doesn't grease them in spite of his complaints.

David
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Old 01-09-2017, 01:18 PM   #20
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I stand corrected. The air comes in through the air filter, is compessed and then i cooled on its way to the intake manifold.
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