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Old 01-30-2020, 04:00 PM   #1
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Cummins 6BTA aftercooler

Just finished having my cooling system serviced. My heat exchangers were in good shape, my after coolers had corrosion and growth on the lower (bottom) part of the tubes. After seeing this, my thoughts are to drain the aftercoolers (by removing the lower zinc) when the boat is going to sit for a few months or longer. This would remove the sea water from the aftercooler core and hopefully minimize growth and corrosion.

Of course this begs the question, is this stupid? is there a downside to doing this? will it really help?

Or the flip side, I am just catching on to what others are doing? Or am I just wiser than others?
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Old 01-30-2020, 04:47 PM   #2
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Well, I think you are wiser. But the corrosion that you saw on the tubes, was it on the inside, the sea water side? I suspect not. It was on the air side. Draining the raw water won't affect that side.

The Cummins after cooler has a design flaw or maybe call it a compromise: the tubes are oriented vertically. The plate that the tubes are rolled into collects condensate on the air side and that condensate with salt from the air sits there and slowly corrodes the aluminum shell. If not serviced routinely that corrosion will break through and let sea water into the air side and get sucked up into your engine.

I don't think that draining the sea water side does much good. That side is all bronze and cupronickle and is very corrosion resistant. It is the air side that is aluminum that is vulnerable.

The best preventative maintenance is to disassemble the air cooler, clean it well, then lubricate it with lots of water proof grease and reassemble with new o-rings.

If you really were talking about corrosion on the inside of the tubes, don't worry about it. It is probably normal sea water flora and fauna and will not affect the tubes.

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Old 01-30-2020, 05:40 PM   #3
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The best preventative maintenance is to disassemble the air cooler, clean it well, then lubricate it with lots of water proof grease and reassemble with new o-rings.

If you really were talking about corrosion on the inside of the tubes, don't worry about it. It is probably normal sea water flora and fauna and will not affect the tubes.

David
I have been told, a .22 cal brush will do a mighty fine job for cleaning the enterior of the tube bundle. I have not tried it.
Currently, the popular method of preventing build up in the coolers is, run the engine weekly and if leaving to boat for a period of time, a fresh water flush.
I guess that means closing the supply hull valve too. That leave the opportunity to fail to open the hull valve when the engine is needed.
I have not read of anyone draining the muffler.
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Old 01-30-2020, 06:56 PM   #4
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DavidM, actually all the buildup and corrosion that I saw was on the raw water side. Thus the idea of draining the raw water out of the cooler.
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Old 01-30-2020, 07:41 PM   #5
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Why not do a fresh water flush if you are leaving the boat for more than couple of days? It only takes a few minutes. Good for the rest of the engine too.
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Old 01-30-2020, 07:42 PM   #6
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If you are going to let your boat sit for that long of a period, the best thing to do is freshwater flush the raw water side. Your entire raw water side (fuel, gear, HX and aftercoolers) will love you for it.
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Old 01-30-2020, 07:51 PM   #7
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Go to TOny Athens' site , Seaboard Marine, and look up his articles about aftercoolers and fresh water flushing.
He has made available a wealth of information about how to set up, service and maintain your Cummins engines.

He is a true expert on Cummins engines, the 6Bs, the 6Cs and all the derivatives.

Much of what he offers is applicable to engines of all mfgrs.


www.sbmar.com
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Old 01-30-2020, 08:15 PM   #8
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DavidM, actually all the buildup and corrosion that I saw was on the raw water side. Thus the idea of draining the raw water out of the cooler.
The raw water side would be INSIDE of each tube...is that what you are talking about? The way you stated it in the first post and what David said made sense. But if they are on the inside of the tubes, just rod them out. OR......you could do an acid flush.
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Old 01-30-2020, 08:55 PM   #9
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Go to TOny Athens' site , Seaboard Marine, and look up his articles about aftercoolers and fresh water flushing.
He has made available a wealth of information about how to set up, service and maintain your Cummins engines.

He is a true expert on Cummins engines, the 6Bs, the 6Cs and all the derivatives.

Much of what he offers is applicable to engines of all mfgrs.


www.sbmar.com

This is the best advice for your issue. Freshwater flushing will save your engine's raw water cooling side, reducing the need to "fully service" all of the components (aftercooler, fuel cooler, gear oil cooler, and heat exchanger).

However, even with freshwater flushing (which I do after each run when there is a decent flow of "dock water" available), the aftercooler will still require a complete "off engine" strip down every 3-4 years and every 2-3 if you don't flush. This is because even running ridlyme etc. through it will not deal with all of the issues. You have several dissimilar metals in contact with one another in saltwater inside the aftercooler (causing corrosion), o rings that could fail allowing salt water into the engine, and the air side gets "gunked up" by the oil particulates that are present in any engine room's air to say nothing about any crank case ventilation system.
Tony explains all of this in great detail on the above mentioned website.
If left without the proper regular servicing, the internal parts will corrode (basically weld) together (ruining the entire unit $$$), the air side will gunk up and start to slowly air starve the engine, and/or the saltwater side could clog up leading to overheating, to say nothing about the potential for saltwater to enter the engine.

After the complete off engine servicing, the aftercooler should be "pressure tested" to ensure no leaking.
To freshwater flush, just replace the sea strainer cap with one that has a garden hose (shutoff) adapter installed. Search for info on Tony's site for photos and how to's. With my setup it takes me about 10-15 minutes from start of getting the hose out to when everything is put away. I don't think just draining the aftercooler will result in much improvement when compared to flushing.
Hope you find this useful
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Old 02-04-2020, 12:59 AM   #10
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Is there no problem with the zinc anodes now that they will be of no benefit sitting in fresh water ?. Or is it that as long as you can be certain that there is no salt present is not a concern ??
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Old 02-04-2020, 01:36 AM   #11
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BeeJay,
You are correct about a zinc anode not being effective in freshwater. It does not erode much during the storage period, but does not seem to affect the metals as long as the aftercooler was reassembled properly using copious amounts of grease per Tony Athen's protocol on the website sbmar.com. If you are still worried about it, you could change them out to magnesium just for the time when there will be freshwater in the unit, or you could go to aluminum anodes.
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Old 02-04-2020, 11:00 AM   #12
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I have been giving some thought to just removing the aftercooler. I have measured the difference in intake air temperature before and after passing through the aftercooler and only see a 10 degree difference at my normal cruise rpm which is below 1800 which is where the turbo starts showing boost. The normal running rpm is 1200 to 1400 on most days. My mechanic indicated I would lose horsepower on the top end, but other than that won’t see any performance differences.

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Old 02-04-2020, 11:43 AM   #13
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You will probably be ok with no after cooler if you run less than 1,800 rpm which as you note has minimal turbo effect. But if you ever try to kick it up higher for any length of time you will probably damage the engine due to high EGT temperatures.


But when it is time to sell, put it all back together. Is it really worth it?


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Old 02-04-2020, 11:48 AM   #14
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You will probably be ok with no after cooler if you run less than 1,800 rpm which as you note has minimal turbo effect. But if you ever try to kick it up higher for any length of time you will probably damage the engine due to high EGT temperatures.


But when it is time to sell, put it all back together. Is it really worth it?


David
Are the non-aftercooled engines any more "fortified" against heat than a aftercooled one(6BT vs 6BTA). Or is the turbo bigger on the aftercooled ones and/or do the generate more boost causing more heat? I guess the real question is right up to the aftercooler and is everything the same after the aftercooler?....the only difference being a cooler air charge and hence more power....
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Old 02-04-2020, 01:57 PM   #15
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At 1800 I am doing 9.3 knots which is more than hull speed. At 2600 WOT I am doing 11.3 knots. I don’t have much reason go over 1800, in fact I don’t have much reason to go over 1500 which is 8 knots. I have run at 1800 in 6’ following seas to improve steering response, but that’s about it. I service the aftercooler every 2 years by removing it, cleaning it, and reassembling it using Seaboard’s service kit. If corrosion ever becomes a problem, then the aftercooler comes out until I decide to replace it.

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Old 02-04-2020, 02:13 PM   #16
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Are the non-aftercooled engines any more "fortified" against heat than a aftercooled one(6BT vs 6BTA). Or is the turbo bigger on the aftercooled ones and/or do the generate more boost causing more heat? I guess the real question is right up to the aftercooler and is everything the same after the aftercooler?....the only difference being a cooler air charge and hence more power....
Both are true.

The 6BTA has a much more robust cooling system to deal with the heat rejection. As a rule of thumb, if burning diesel makes 1 btu of heat, 1/3 goes into rotational energy, 1/3 out the exhaust and 1/3 out in the cooling system. So if a 6BT produces X btu/hr out of the exhaust or cooling system, the 6BTA will produce 370/210= 1.76*X

The turbocharger produces much more boost than the non aftercooled 6BT engine to have enough air to let you inject more fuel to make more hp.

So at a maximum boost of about 30 psi, the air in a 6BTA gets up to 500 deg F or so at wot. The aftercooler drops that down to maybe 100. With no aftercooler and 500 deg intake air, the engine's egt will go crazy and melt pistons and valves.

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Old 02-04-2020, 02:22 PM   #17
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Thanks for the info David!!!
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Old 02-04-2020, 03:06 PM   #18
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BeeJay,
You are correct about a zinc anode not being effective in freshwater. It does not erode much during the storage period, but does not seem to affect the metals as long as the aftercooler was reassembled properly using copious amounts of grease per Tony Athen's protocol on the website sbmar.com. If you are still worried about it, you could change them out to magnesium just for the time when there will be freshwater in the unit, or you could go to aluminum anodes.

I don't understand this. My 6bta has zinc anodes and is in 100% fresh water. I replace them as needed as they erode as they are intended to.
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Old 02-04-2020, 03:08 PM   #19
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I have been giving some thought to just removing the aftercooler. I have measured the difference in intake air temperature before and after passing through the aftercooler and only see a 10 degree difference at my normal cruise rpm which is below 1800 which is where the turbo starts showing boost. The normal running rpm is 1200 to 1400 on most days. My mechanic indicated I would lose horsepower on the top end, but other than that won’t see any performance differences.

Tom
How are you measuring these temperatures? And what are they ? And what is the ambient air temperature in your ER comparatively?
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Old 02-04-2020, 03:12 PM   #20
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At 1800 I am doing 9.3 knots which is more than hull speed. At 2600 WOT I am doing 11.3 knots.

Tom

I was out this weekend. I got 14.1 knots @2580RPM wot with full tanks and a dirty bottom. If that is typical performance for your NT37, something else is going on.
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