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Old 09-15-2018, 04:00 PM   #1
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Cummins QSB 5.9L Fresh water flush

There have been other threads on this but rather than dig up an old one, I started this.


After wanting to do this for several years, I finally got around to doing something about it.


I ordered one of these . I tried it out for the first time last night when we got back from our 2 week trip.


My hope was that eventually I would be able to connect a hose to this, leave the seacock open, turn on the hose full and run the engine. My thought was that the water pressure would back flush out the seacock and give the engine enough fresh water. My only question was whether the flow from the hose would be sufficient to displace the raw water and supply the engine.


To test this out I filled up a 5 gallon bucket with fresh water, attached a 5' length of hose from the strainer cap to the bottom of the bucket, closed the seacock, and started the engine. The engine drained the bucket in less than a minute!


So, I turned off the engine, refilled the bucket, and this time kept the fresh water hose filling the bucket while I started the engine. This time, the engine emptied the bucket in about 1/2 the time it did prior without the dock hose trying to keep the bucket full. A very rough guess is that I could probably supply about 10 gallons of flush water by keeping the dock hose running, start with a full bucket, and run the engine until the bucket empties.



This told me that the dock hose didn't have adequate flow to keep up with the engine's water pump and therefore my initial plan was not going to work.


So now to questions for you smart people.


1. How much water is needed to flush/replace the raw water in the Cummins heat exchanger and after-cooler? Would 10 gallons be adequate.


2. Am I missing other options?
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Old 09-15-2018, 04:31 PM   #2
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Ten gallons is plenty. I use 5 in a Detroit. Using a dock hose will work, but nobody else will have water until you shut off the engine.

Install a tee, valve and hose fitting between your salt water pump and the sea cock. My tee is right after the sea cock so the strainers are flushed, too. Close the sea cock, open the new valve, and at idle you move enough water so you don't damage the impeller. If I'm going to anchor in salt water for an extended period, I flush my engines. I winter in fresh so it's not an issue.

Sometimes I do maintenance at anchor and the new tee and valve along with another on the exhaust water makes doing a chemical flush easy. I either use the salt water pump at idle (chemistry works better at engine temperature) or use a bilge pump in the bucket and take out the impeller. Gotta watch the temp, 5 gallons won't cool a diesel, even at idle, for too long.
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Old 09-15-2018, 05:29 PM   #3
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Ten gallons is plenty. I use 5 in a Detroit. Using a dock hose will work, but nobody else will have water until you shut off the engine.

My concern is that at my dock, the flow from the dock hose can't keep up with the Cummins water pump. The hose would likely collapse and leave the impeller running dry.
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Old 09-15-2018, 05:34 PM   #4
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Would doing this twice for a total of 20 gallons work?
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Old 09-15-2018, 05:41 PM   #5
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I think 10 gallons works...I have a Y-valve with a 3 foot length of rigid hose...I fill two 5 gallon buckets...put the hose in one and as it is drawn down I pour the other bucket in and go turn the motor off. At the last service the tech said the inside of the cooler looked new. I like the idea that the engine is pulling the fresh water in on its own vs. dock or hose pressure. We've been doing this anytime we're stopped longer than one night.
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Old 09-15-2018, 05:47 PM   #6
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Dave:

If you can supply ten gallons from a bucket with a hose refilling it, that is more than enough to flush the engine. For comparison on my Yanmar 5.3 liter 370 which is about 10% smaller than the Cummins, I get a strong pink froth out of the exhaust after pulling less than 3 gallons of antifreeze through the engine.

So, even allowing for some back mixing, 10 gallons should be plenty.

OTOH I have flushed that engine many times, by closing the seacock, hooking up a hose and running the engine for 5 minutes. Yes the hose collapses but so what, it is still flowing water through it. And my dock water pressure is probably lower than yours. It will not fill a 5 gallon bucket in one minute.

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Old 09-15-2018, 05:52 PM   #7
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Just get the wife to shut it down, refill bucket, crank it up etc etc.
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Old 09-15-2018, 06:33 PM   #8
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Dave:

If you can supply ten gallons from a bucket with a hose refilling it, that is more than enough to flush the engine. For comparison on my Yanmar 5.3 liter 370 which is about 10% smaller than the Cummins, I get a strong pink froth out of the exhaust after pulling less than 3 gallons of antifreeze through the engine.

So, even allowing for some back mixing, 10 gallons should be plenty.

OTOH I have flushed that engine many times, by closing the seacock, hooking up a hose and running the engine for 5 minutes. Yes the hose collapses but so what, it is still flowing water through it. And my dock water pressure is probably lower than yours. It will not fill a 5 gallon bucket in one minute.

David


Thanks. I guess I was concerned about not supplying the engine with enough water. It didnít occur to me that while it isnít supplying as much as the engine would normally take, it is still supplying water.

The other thing I am trying to do is figure out how to manage it all. In my boat, the forward part of the ER is accessed by lifting the stairs from the saloon down to the hallway at the bottom of the boat. This is great access but it means that I have to close that access to go from the ER to the pilothouse or even exit the boat.

I am also trying to come up with a system that I can do this simply without any assistance.

So, if hooked up the hose to the strainer and then exited the boat and turned the hose on full. Since the seacock would be open, there is no danger of forcing water through the cooking system as it would simply exit via the seacock. I could then board the boat and start the engine. Then go to the ER and close the seacock and let the engine run for a few minutes.

The only problem is shutting it down. If I shut the engine down, then I have the fresh water getting pressurized until I could either get to the seacock to open it, or get to the hose bid to shut it it off. Iíd be worried about what damage forcing the water into the engine cooling system while it isnít running. Alternatively, I could open the seacock and then try to quickly shut the engine down before it sucks raw water into the system.

That makes using a bucket a more attractive option. I can set it up in the ER, place the dock hose in the bucket and close the seacock. I then can easily open the hose bib, board the boat and I can see the bucket in the ER by looking down from the PH stairs. Then the bucket is almost full I can start the engine and then watch the bucket until it is almost empty and then shut the engine down and quickly exit the boat and turn off the water. Again, Iím guessing that would give me about 10 gallons through the engine.
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Old 09-15-2018, 06:40 PM   #9
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Just get the wife to shut it down, refill bucket, crank it up etc etc.

That is what I did yesterday. That works but my wife doesnít move as quickly as I do and I would like to have a system that I could do solo.

I also noticed that yesterday I ended up restarting the engine 2 times. The first was when I was just going from the bucket, and the second when I had the hose running into the bucket. Normally, my engine takes 1-2 seconds to start. The second time I restarted it, it took about 4 seconds to start. Not a big deal, but Iím not sure that starting and the stopping the engine a lot is all that good for it.
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Old 09-16-2018, 12:04 AM   #10
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My boat also has a QSB and a fresh water flush connection. I've not had a chance to use it yet, but expressed those concerns to the P.O. who used it routinely before he moved the boat to fresh water.

There are two concerns: does the pressure from the water main create a problem (if the seacock is closed); and does the hose supply enough for the engine?

According to the P.O., he closed the seacock, started the engine and simultaneously turned on the hose. As long as the engine was kept at idle or just above, flow was adequate from the hose. When he shut the engine he shut the hose. He had a similar setup on the genset, in that case he ran the hose only half on, the genset of course ran at full rpm (NL, 1800). He reported no problems using this technique.
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Old 09-16-2018, 01:43 AM   #11
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Leave the seacock open when flushing. As mentioned above, excess will just run out the seacock before/after starting/stopping engine.
If your dock hose doesn’t provide all that the raw water pump demands, it will draw some salt water, but the salt will be generously diluted, still far better than not flushing.
If you have fresh water tanks onboard, use them for engine flush water flush, they will benefit from more frequent cycling!
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Old 09-16-2018, 08:31 AM   #12
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Quote:
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2. Am I missing other options?

I didn't read the whole thread closely, but FWIW when I flushed our 450Cs, I didn't use the on-engine raw water pumps. Instead, I used a transfer pump.

I also did each engine slightly differently. One, I recirculated the product (Rydlyme, in that case). The other, I filled the raw-water system and let it sit, flushed later. Didn't see any difference in final outcome.

The latter turned out to be slightly easier for me, because it's not so easy for me to disconnect or pinch off the feeds to our dripless shaft seals. With the recirc version, I felt like I was losing too much product to the shaft seals...

Also, I wouldn't have needed as many fittings for the recirc version. I simply backfilled from the heat exchanger outlet until product reached the top of our aftercoolers. Zincs removed and replaced with blank plugs, with the upper aftercooler zinc fitting open -- for air relief and to know when to stop filling.

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Old 09-16-2018, 11:01 AM   #13
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My boat also has a QSB and a fresh water flush connection. I've not had a chance to use it yet, but expressed those concerns to the P.O. who used it routinely before he moved the boat to fresh water.

There are two concerns: does the pressure from the water main create a problem (if the seacock is closed); and does the hose supply enough for the engine?

According to the P.O., he closed the seacock, started the engine and simultaneously turned on the hose. As long as the engine was kept at idle or just above, flow was adequate from the hose. When he shut the engine he shut the hose. He had a similar setup on the genset, in that case he ran the hose only half on, the genset of course ran at full rpm (NL, 1800). He reported no problems using this technique.

Those two concerns you mention are concerns that I shared. I discovered that my dock hose wonít supply too much water for the engine if the seacock is closed. However, that leaves the second concern.

Your PO said that he simultaneously turned on the hose and started the engine and did the reverse when finished. I want to be able to do it solo, which means that I canít simultaneously close or open the hose bib while starting or shutting down the engine.
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Old 09-16-2018, 11:08 AM   #14
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Originally Posted by ranger42c View Post
I didn't read the whole thread closely, but FWIW when I flushed our 450Cs, I didn't use the on-engine raw water pumps. Instead, I used a transfer pump.



I also did each engine slightly differently. One, I recirculated the product (Rydlyme, in that case). The other, I filled the raw-water system and let it sit, flushed later. Didn't see any difference in final outcome.



The latter turned out to be slightly easier for me, because it's not so easy for me to disconnect or pinch off the feeds to our dripless shaft seals. With the recirc version, I felt like I was losing too much product to the shaft seals...



Also, I wouldn't have needed as many fittings for the recirc version. I simply backfilled from the heat exchanger outlet until product reached the top of our aftercoolers. Zincs removed and replaced with blank plugs, with the upper aftercooler zinc fitting open -- for air relief and to know when to stop filling.



-Chris

Thanks Chris. Good ideas when/if I want to flush with a product such as Rydlyme. What Iím trying to do is to flush the engine with fresh water after every use. The idea is to replace the salt water with fresh to limit the amount of corrosion in the heat exchanger and aftercooler. So I need a technique that is easy, simple, and quick enough to be able to do every time I return to the dock.
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Old 09-16-2018, 11:15 AM   #15
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Dave. I must have gotten a good nights sleep, because this idea just popped into my mind. Why not borrow your boat neighbors hose, and use 2 hoses to fill the bucket. Throw in a little salt-away, and that QSB will be very happy.
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Old 09-16-2018, 11:42 AM   #16
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Dave. I must have gotten a good nights sleep, because this idea just popped into my mind. Why not borrow your boat neighbors hose, and use 2 hoses to fill the bucket. Throw in a little salt-away, and that QSB will be very happy.

Good idea Dan. Iíll have to look at that....
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Old 09-16-2018, 02:42 PM   #17
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Hose size and length makes a big difference in flow. So the shortest length of 3/4 hose, will flow a heck of a lot more water than same size 1/2 or 5/8 inch hose. These are the most common size of garde hose available. Google flow rates, the numbers are surprising. D
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Old 09-16-2018, 02:54 PM   #18
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Save you the work Dave.
12 gal 1/2 in @40# 50ft. 25 gal 1/2 in 25 ft
22 gal 5/8. 44 gal 5/8
36 gal 3/4. 72 gal
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Old 09-16-2018, 08:01 PM   #19
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Dave:

This is how I do it single handed:

Start the engine with the hose connected to the flush fitting with the water valve on and the seacock open. Close the sea cock. The hose collapses a bit as the raw water pump pulls more than the hose can supply, but plenty enough to keep the engine cool at idle. Run the engine for 5 minutes. Close the hose water valve and immediately shut down the engine. Open the seacock.

This flushes the engine and never puts excessive water pressure on the raw water pump. The 10-20 seconds that it takes me to close the engine room hatch (I need to close it to get to the helm) and shut down the engine doesn't hurt a thing.

In my case the engine can pull something like twice the volume of water as the hose can supply. So if you left the seacock open and tried to flush it that way, it would get a mixture of 50/50 sea and fresh water. Not so good. This way you get 100% fresh water and after 5 minutes all of he sea water has been displaced from the engine. I have tested this by pulling zincs at various places along the water path and all tasted fresh.

I have even flushed at a mooring with no dock water available by using the potable water system. The potable water pump puts out even less water so I run it a bit longer, maybe ten minutes to displace all of the sea water.

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Old 09-16-2018, 08:32 PM   #20
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Many dock water systems, city water included contain various salts and minerals, as well as chlorine, none of which are great for your cooling system, but that’s what sits in your raw after system after a flush.
So if you’re a purist, you’ll insist on flushing with only distilled water only!
Most of the commercial fishing boats I’m familiar with never flush their raw water systems, and they get many thousands of hours out of them without a problem.
Regular use decreases the importance of flushing, as it’s the downtime that causes the damage.
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