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?

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.

Lepke said:

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.

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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.

Would doing this twice for a total of 20 gallons work?

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.

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

Just get the wife to shut it down, refill bucket, crank it up etc etc.

djmarchand said:

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

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Thanks. I guess I was concerned about not supplying the engine with enough water. It didn’t occur to me that while it isn’t 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. I’d be worried about what damage forcing the water into the engine cooling system while it isn’t 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, I’m guessing that would give me about 10 gallons through the engine.

Rebel112r said:

Just get the wife to shut it down, refill bucket, crank it up etc etc.

Click to expand...

That is what I did yesterday. That works but my wife doesn’t 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 I’m not sure that starting and the stopping the engine a lot is all that good for it.

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.

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!

dhays said:

2. Am I missing other options?

Click to expand...

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

DDW said:

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.

Click to expand...

Those two concerns you mention are concerns that I shared. I discovered that my dock hose won’t 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 can’t simultaneously close or open the hose bib while starting or shutting down the engine.

ranger42c said:

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

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Thanks Chris. Good ideas when/if I want to flush with a product such as Rydlyme. What I’m 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.

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.

Rebel112r said:

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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Good idea Dan. I’ll have to look at that....

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

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

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.

David

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.

Although quite expensive these people have some very nice kits you can install to flush your engines. https://aditmarine.com.au/

Some friends of our have one of their products installed and are very happy with it. I used to flush our little 40 series Volvo's using just the dock hose through a tee fitting and turning the seacock's off but our Cummins were never shut down long enough to have a great benefit.

dhays said:

Those two concerns you mention are concerns that I shared. I discovered that my dock hose won’t 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 can’t simultaneously close or open the hose bib while starting or shutting down the engine.

Click to expand...

My concern with the seacock closed would be pressurizing the raw water system with 80 psi city main pressure. The PO of my boat always had his wife to help. I like the sequence described by David above.

I'm not too worried about undersupply of water at idle. It doesn't seem to hurt the pump to even have the seacock closed for periods of time, and a hose surely supplies enough to cool at idle - but you could watch the temp and see.

How much hose pressure would a raw water pump need, for any damage to occur? Next time I have the pressure washer revved up I will try to find a Raw water impeller and some way to immobilize it so I can see if 3200# pressure is enough.
Somehow I doubt 60# street pressure will do anything at all.

Rebel112r said:

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

Click to expand...

Thanks Dan.

djmarchand said:

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.

David

Click to expand...

Thanks David. That is what I needed to know. It would be easier if I had an engine shut off there in the ER, then I could just shut the engine off and open the seacock at the same time.

koliver said:

How much hose pressure would a raw water pump need, for any damage to occur? Next time I have the pressure washer revved up I will try to find a Raw water impeller and some way to immobilize it so I can see if 3200# pressure is enough.

Somehow I doubt 60# street pressure will do anything at all.

Click to expand...

I don’t think it is a problem on the impeller, but I really don’t know. Maybe David or some of the other smart diesel folks can tell us?

dhays said:

I don’t think it is a problem on the impeller, but I really don’t know. Maybe David or some of the other smart diesel folks can tell us?

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Since the raw water pump seal is designed to operate at a slight vacuum, I think any positive pressure could blow out the seal.


David

dhays said:

Thanks David. That is what I needed to know. It would be easier if I had an engine shut off there in the ER, then I could just shut the engine off and open the seacock at the same time.

Click to expand...

Dave:

I don't know about your Cummins, but my Volvos shut down if I grab the throttle at the high pressure pump and hold it closed. No fuel and it shuts right down. I could reach the throttle with one hand and the seacock with the other. Doesn't work for startup of course, but then startup is less time sensitive.

koliver said:

How much hose pressure would a raw water pump need, for any damage to occur? Next time I have the pressure washer revved up I will try to find a Raw water impeller and some way to immobilize it so I can see if 3200# pressure is enough.
Somehow I doubt 60# street pressure will do anything at all.

Click to expand...

I'm not worried about the pump though you could blow the seal. But you are pressurizing the entire raw water circuit to 60 or 80 psi. Strainer, hoses, heat exchangers, exhaust elbow, muffler. It is certainly not built to take that pressure, and you might find out that it won't. Now, it is open at the far end and there are some restrictions on the near end which will reduce the pressure some, maybe a lot, and that *might* mitigate the pressure depending on the boat.

In addition, you are adding water in an uncontrolled amount to the muffler. If the engine stops, you are still adding water. It doesn't take long for a waterlift muffler to fill up, after which it fills the turbo, exhaust manifold, and cylinders. Then the oil sump.

I'd much rather see the engine somewhat starved for water in this scenario than have too much. If it is starved, you will see the temperature climb slowly. With too much, you may not know until something is very wrong.

The sequence David described eliminates many of these concerns. With the seacock open, excess pressure will exit the thru hull. Turn on the hose, then turn off the seacock with the engine running.

I don’t think the system would see those pressures, the water from say a 3/4 inch hose is free to exit out of a much larger exhaust. If you plugged the exhaust, you would have that problem after it filled several cylinders with water!.