Cummins QSB 5.9L Fresh water flush

My first power boat had a unique flush system. The previous owner had converted the salt water anchor wash to a fresh water flush line as the through hull came from the engine room. Then he had an alternate system the drew from the fresh water tanks. He could flush at anchor and at the dock. My thinking is, just draw from the fresh water tanks and refill them at the dock. The sequence was, start the engines, turn on the water, close the sea cocks, turn off the water, stop the engines, open the sea cocks or not. I don't remember if I did both engines at the same time or individually. I think it was both. That boat held 300 gallons of fresh water so we could flush at anchor but I never did.

My new boat has no flush. I'm going to tap into the fresh water tanks and refill at the docks.

RickyD said:

My first power boat had a unique flush system. The previous owner had converted the salt water anchor wash to a fresh water flush line as the through hull came from the engine room. Then he had an alternate system the drew from the fresh water tanks. He could flush at anchor and at the dock. My thinking is, just draw from the fresh water tanks and refill them at the dock. The sequence was, start the engines, turn on the water, close the sea cocks, turn off the water, stop the engines, open the sea cocks or not. I don't remember if I did both engines at the same time or individually. I think it was both. That boat held 300 gallons of fresh water so we could flush at anchor but I never did.

My new boat has no flush. I'm going to tap into the fresh water tanks and refill at the docks.

Click to expand...

Interesting. I can switch from raw water to fresh water on my washdown pump. However, my system doesn’t have the same comparable fresh water flow that even my wimpy dock hose has.

However, I can see a couple of possibilities for using the fresh water from my tanks...

I just used the fresh water flush on the hard to test the engine and new cutlass bearings. With the hose on (and good pressure from the mains) at idle the suction from the engine collapsed the hose. So no worries about it providing too much pressure. I turned the hose on with the seacock open, started the engine, then shut the seacock.

I dealt with this on a previous boat. A little different situation because I was winderizing, but the same in that I needed to replace the sea water circuit with something other than sea water.


I used the same type of strainer cap with a hose fitting, except it was before Groco offered them and I had to make it myself from a replacement bronze cap.


I also made a general purpose "service" bucket that has come in hand over and over again. It's just a 5 gal bucket, and I installed a fitting and shutoff valve through the side of the bucket as close to the bottom as possible. That allows water to be drawn from teh bottom of the bucket rahter than pulled up over the top. for flushing something like an HVAC pump that has no lift capability, it allows you to gravity feed it.


OK, with that aside, I needed to flush prop glycol through the system, not just water, but the approach is the same. I did as you and closed the thruhull and filled the bucket. Then start and run the engine which would drain the bucket down very fast. Stop when the bucket is empty, refill, and repeat.


That flushes with 100% of whatever you put in the bucket. Getting back to your original question, my engines were QSCs, not QSBs, so a bit larger. And I also needed to get glycol into the muffer, not just the engine. So I needed more juice than you need to just get fresh water into the engine and the injection ring. I needed 15 gal per engine, and I think a significant part of that was the mufflers. So I would think 5 gal would probably be plenty for you, and 10 gal would be certain beyond any doubt.


I would not operate with the thruhull open. That just defeats the whole purpose.


You could run the hose to keep filling the bucket while draining, but that makes for a very difficult one man job. If you fill the bucket, shut off the hose, go start and run the engine long enough to drain the bucket, then go fill up again, it's an easy one man job. I always did it myself on our boat.


I would also let the engine pull water from the bucket, and never connect the hose such that the raw water system is pressurized. Not only do you risk damage to teh impeller, but you can full the muffler (assuming a water muffler) more than expected and risk back flooding the engine. It's not a certain problem, but an opportunity to make mistakes, forget to turn off the water, or whatever.

Hi,


Have you seen this video where QSB built fluch system?




NBs

North Baltic sea said:

Hi,


Have you seen this video where QSB built fluch system?

NBs

Click to expand...

Thanks for that NB. Looks like they just stuck a hose in a large diameter hose. That avoids any risk of pressurizing the system.

I was surprised that they were running the engine at 760 rpm. Idle for these engines is 600 rpm. I don’t see any reason for flushing the engines at higher than idle.

Twisted, thanks for your experience. What you did was pretty similar to what I ended up doing and I think will likely continue to do for the mean time.

Part of the issue I have is that I need to make the process as quick and convenient as possible. Unfortunately, getting access to the front of the engine means flipping up the stairs thereby blocking the way to the pilothouse. So I have attached a line that I can use to lift the stairs from above.

If I had an engine shut-off in the ER, near the front of the engine, it would be easy. I could attached the hose directly to the filter cap with the thru hull open. Turn on the hose, then turn on the engine. I could then open the thru hull and turn off the engine from the ER. Unfortunatley, I can’t do that.

So...
- attach short hose to the filter with the end placed in the bottom of a 5 gallon bucket.
- Place the end of the dock hose in the bucket.
- close the stairway access, climb the stairs, pull the line to open the stairs (I can now see down directly into the bucket in the ER)
- get off the boat and open the dock water valve
- quickly reboard the boat and stand at the back of the PH and look down at the bucket.
- start the engine when the bucket is full.
- watch the bucket and stop the engine as the bucket approaches empty.
- turn the engine on again when the bucket is almost full and again turn it off when the bucket is almost empty.
- quickly exit the boat and close the dock water valve.
- open the engine thru-hull

I just need to be quick enough to turn off the dock water before the bucket overfills and gives my bilge a fresh water flush.

As in the video that was posted, I could put another hose section and in-line shut off in the line, but that would decrease the flow from the hose.

Not that anyone is all that interested, but I tried the above today.

I attached the hose directly to the filter with a shut-off near the helm. I closed the seacock, started the engine, and turned on the hose and let the engine run for 5 minutes or so. Then turned off the hose and shut the engine down.

The hose didn’t collapse but was very “soft”. With just my thumb and forefinger I was able to squeeze the hose closed. So my ignorant assumption is that the hose wasn’t quite able to keep up with the water demand from the engine water pump but not enough of a water deficit to collapse the hose.

That's just what mine does. I don't think you are actually going to cut off water to it, after all there is still pressure in one end of the hose. Just a lot of pressure drop by the time it gets to the end.