The case for fresh water engine flushing

[DavidM]

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

 

[tadhana]

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.

 

[Ski in NC]

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.

 

[smitty477]

"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"

 

[tadhana]

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.

 

[Ken E.]

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.

 

[DavidM]

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

 

[cardude01]

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?

 

[Ski in NC]

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.

 

[Larry M]

Performance Metals makes/sells aluminum pencil anodes. No more broken pieces lost in the cooling system.

Rudder Trim Tab Anodes

 

[tadhana]

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!

 

[smitty477]

"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/47b5df07b3127cceca60c455dd5100000010O08AcN2rNq4btQe3nwQ/cC/f%3D0/ls%3D00005785357820050127014411185.JPG/ps%3D50/r%3D0/rx%3D550/ry%3D400/


https://im1.shutterfly.com/media/47...0050127014339081.JPG/ps=50/r=0/rx=550/ry=400/

 

[sunchaser]

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.

 

[sunchaser]

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.

 

[tadhana]

Sunchaser, I suppose might, but I did run a Cummins and Yanmar marine engine service center.

 

[Ski in NC]

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.

 

[smitty477]

"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?

 

[tadhana]

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.

 

[DavidM]

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

 

[tadhana]

I stand corrected. The air comes in through the air filter, is compessed and then i cooled on its way to the intake manifold.

 

[smitty477]

"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."


You are looking at cast bronze and cupronickel parts there is no aluminum within this assembly. The open parts show the raw water sections and pathway only - at the base of the air side path there are no "O" rings at all. But there is a 'space' in height where the water and blowby can collect (if any) this area has a drain and inspection plate that can be utilized if/as necessary.
These intercoolers are installed on boats that have seen more than 30 years of use and I have never heard of a failure or problem with service with any of them.

 

[DavidM]

I didn't realize that the after cooler body in your pic is bronze. What engine is that on. It must weigh a lot!!!

David

 

[sunchaser]

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.


David

David

You are correcting the wrong guy. I pointed out to a Cummins and Yanmar dealer and supposed expert that he did not know which end of the after cooler goes where.

 

[smitty477]

"I didn't realize that the after cooler body in your pic is bronze. What engine is that on. It must weigh a lot!!!"


Hello David - Although I have had more than a few out to clean them I never weighed one. Perhaps 20-25 pounds when empty I guess. The entire engine weighs in at 1,250 dry - Hino WO6 series.

 

[Duvie]

Perkins multicoolers

I went through both my Perkins multicoolers last Winter. I had corrosion issues in the aluminum in the area of the o-ring seal not only in the after cooler sections but also the oil cooler sections of the multicooler. I believe that the o-rings over time take a set and allow the salt water to touch the aluminum. As soon as this happens the condition progressively gets worse due to corrosion until you have a failure. I think that setting the o-rings in place with a high quality waterproof grease and a maintenance plan to disassemble, re-grease and replace the o-rings on some schedule is the way to go.

I do not believe that flushing with fresh water will help much as the problem starts in very tight edges/corners of the o-ring joint and any salts in these areas are not likely to be washed away. they are in a sense trapped under the o-ring.

 

[Fletcher500]

Flushing the salt is good, but a few comments..

The flush connection must be bullet proof, as far as breakage or it could cause much larger issues.

An operator who flushes, and forgets to secure the system could cause damage.


You can't do this on engines under warranty because it will probably void it if big brother finds out.

What about rydlime or barnacle buster or similar decalcificaion solutions? I.E., many people do this annually at the dock, in a controlled environment, and appear to get very good results, hence the flush after very use can be avoided.

 

[DavidM]

What about rydlime or barnacle buster or similar decalcificaion solutions? I.E., many people do this annually at the dock, in a controlled environment, and appear to get very good results, hence the flush after very use can be avoided.

This is mostly conjecture, but it is backed up with some theory and a little bit of experience:

Calcification only occurs during running. Why? Because it is heat that precipitates the calcium/magnesium compounds present in sea water out on the heat exchanger surfaces. Calcification will not occur in engines just sitting at the dock. Critters may grow (see below) but calcium compounds will not precipitate on cold metal. Take a look at your bronze rudder. It has barnacles on it, but no calcium deposits.

Fresh water flushing is almost entirely for corrosion mitigation, and is not expected to help with calcification. Fresh water flushing does do some good for marine critters. Marine critters were bred to thrive in a salt water environment. When a few critters are left in an engine after use but their environment is changed to fresh water, they die.

So bottom line, I consider fresh water flushing and periodic acid flushing with Rydlyme, etc. complimentary, but one will not suffice for the other.

And BTW I would acid flush only every 5 years or if I see temps rising at wot, not every year. Too much corrosion for yearly use.

David

 

[dhays]

Configuring a fresh water flush is something that I have wanted to do since I bought the boat. I have a Cummins 5.9 QSB. It has the vertically oriented aftercooler. I had it removed and serviced shortly after I bought the boat since it had never been done in its 6 years and 773 hours of life.

I was hoping that doing a fresh water flush would help extend its lifespan, and like David, thought that it could extend the times between servicing of the aftercooler. Given the information that the corrosion may come from the air side and not the raw water side, makes me less inclined to do it.

After looking at lots of options for a fresh water flush, I had decided that for my boat a system such as this would work the best for me. I didn't want to have to swap out the top of my sea strainer each time and the location in the ER means I can't leave any fittings in place on top of the strainer. My plan was to use the above fitting and run a hose to the stern with a hose fitting. Then flushing would be as simple as connecting the fresh water hose from the dock and then opening the valve while the engine is idling.

It would be a bit of grunt work to setup however, and if it won't really affect the ultimate problem , then I likely will give up on the idea and simply look at doing a yearly flush with some kind of descaler.

 

[CMS]

I have commercial lobstermen using the same Cummins, Cat etc. engines (though mostly no turbo's) and I have numerous engines in excess of 15 years old and 8000 - 18,000 hours that have never ever been fresh water flushed. I can't recall the last time I replaced a core pack or HX due to corrosion. For these guys the engines will rust through from the outside before they corrode from inside. I have some that are so rusty it is hard to even tell brand color but the salt water cooling circuit still works......

Never flushed, no corrosion in the raw water circuit requiring HX replacement.. IIRC this engine is a 1986 vintage..

Be aware that on certain installations incorrect flushing (pressure feeding the RW inlet) can lead to hydrolocking the engine and potentially destroying the engine.

I know of two boaters who bought the Forespar flushing valve and direct connected a garden hose to it thus hydrolocking their engines. One engine was ruined the other badly flooded.....

 

[Fletcher500]

So bottom line, I consider fresh water flushing and periodic acid flushing with Rydlyme, etc. complimentary, but one will not suffice for the other.

And BTW I would acid flush only every 5 years or if I see temps rising at wot, not every year. Too much corrosion for yearly use.David

It appears you have done your homework on the subject, but I still question this and would think a descaler can take care of all of the build up inside the raw system. The fact that it runs through the entire system and wil clean the rubber hoses as well is a plus.

It is not common in my area, but apparently quite a few people on the east coast use it.

Agree, yearly is probably overkill, but how do you know it will cause corrosion? I have not used it, but from what I have read it is a fairly mild solution and no one has reported corrosion issues. We pulled apart the coolers on our 2.5 year engines and it is starting. I am therefore leaning to every few years, but still trying to figure out how to get it through the drives..long story.