Flushing raw water system with fresh water

[BobHorn]

A PO has teed a fresh water connection, through a valve, into the raw water input to the raw water strainer. According to the PO's wife, he is no longer with us, this was to allow flushing the various coolers and especially the exhaust system with fresh water.
Anybody ever heard of doing that? Almost seems like a good idea if the boat is not run for a while.


Bob

[sailormed]

Whatever you do, NEVER connect tap water directly to the input valve on the engine. Attach a short hose to the engine that goes to the bottom of a bucket. Fill the bucket with the hose from the tap. This way you will not flood your engine.

[BobHorn]

This is to flush the raw water side, not the engine coolant.

[desodave]

Have a look at the similar threads shown below and you'll see that a number of people do similar things. I have read another thread recently however suggesting that you should not use pressurized water - rather run the water into a bucket and let the engine impeller pick it up.

https://www.cruisersforum.com/forums...ay-190232.html
This wasn't that thread but is a similar one. You may want to do a little more research before using or hope that some of the more experienced people chime in here.

[dougweibel]

I did this with the generator on my last boat at the recommendation of a Fischer Panda rep. I agree with the comment above to not hook into a pressurized fresh water supply but rather use a hose into a bucket of fresh water and let the engine/generator's raw water pump suck in the water.

[Sailmonkey]

Originally Posted by BobHorn

This is to flush the raw water side, not the engine coolant.

That’s the danger. If the hose overwhelms the exhaust, and fills the muffler....etc, then the water fills the engine through the exhaust.

[flyingfin]

I had vessel with brass hose bibb attachment after raw water strainer. Process to use was:
1. Connect fresh water hose to the hose bibb via used washing machine hose and turn on fresh water supply. dock hose pressure will dictate how much fresh water pressure to allow in the supply hose
2. Start engine
3. Open brass hose bibb attachment, this introduces fresh water to the raw water cooling system while also backflushing the raw water strainer and raw water intake valve.
4. Close sea cock valve that serves engine raw water intake and sea strainer
5. continue to run engine for one minute
6. Turn off engine and fresh water supply at same time.
7. Put engine key on raw water seacock handle.

[BobHorn]

I think unless there is extreme pressure from the fresh water system, the raw water impeller will control the amount of water. I was just curious to see if other people had something similar.

[Sailmonkey]

Originally Posted by BobHorn

I think unless there is extreme pressure from the fresh water system, the raw water impeller will control the amount of water. I was just curious to see if other people had something similar.

It won’t. The water pressure from a standard garden hose will run through a an impeller pump when the engine isn’t running.

Just be aware that with the engine off and the hose on, you’ll be filling the exhaust.

[Jackz]

I simply put fresh water in a bucket and have a portable bilge pump that circulates the water through the heat exchanger back into the bucket. Just remove the input and output hoses on to/from the heat exchanger

[waterman46]

Originally Posted by BobHorn

This is to flush the raw water side, not the engine coolant.

The following is fairly common knowledge, but for anyone who wasn't aware of it:

If you let pressure water either from the raw water pump or a fresh water pressurized flush, into the raw water system long enough, when the engine is not running, then the excess water will flow through and out of the heat exchanger, into the exhaust system at the tee and fill up the water lift muffler since the engine is not running to push it out the exhaust hose. After that happens the pressure water will back up into the exhaust manifold and into one or more cylinders. Next time you start engine, if it can fire on one cylinder you may break parts of the piston and connecting rod assembly in the cylinder that had water in it.

[Tugwit]

Originally Posted by BobHorn

...
Anybody ever heard of doing that? Almost seems like a good idea if the boat is not run for a while.

Bob

It is a good idea. It mitigates corrosion and biological fouling in the heat exchanger(s) when, as you say, the boat is not run for a while. It can also be used to conveniently introduce an antifreeze mixture into the raw water side during a winter lay-up.

Rather than a tee, I installed a Forespar Marelon 931233 seacock for that purpose. This is a dual-inlet valve: with the handle in one position, it pulls raw water from the sea, and with the handle in another position, it pulls water from a separate port inside the boat--which is connected to a short length of hose to insert in a bucket of fresh water (or antifreeze mixture) for flushing. (With this dual-inlet valve, the valve is closed with the handle in the vertical position.)

It works great--and I concur with other responders that using a bucket is the safe way to go. You can leave a shore-side water supply hose running into the bucket while you're operating the engine and flush the system for as long as you want (so long as you match the flow in to the flow out! ).

I installed a similar system in the head intake seacock. A fresh-water flush of the head (with perhaps a drop of chlorine bleach in the bucket) prevents marine organisms from dying and decomposing in your toilet flush water--which otherwise stinks up the boat in a short time. Also works great.

Overall, it adds maybe five minutes to the post-cruise routine when the shore-side hose is already out for a rinse-off.

[bailsout]

My tee is on the engine side of the strainer. I used the pressured water from the dock but I put it on a slow flow. After a couple of minutes I taste the exhaust water for salt. I know, but I’m Not dead yet and I often taste my bilge water after a rain!

[oldcal46skipper]

I will take photos tomorrow and post my simple solution that has worked for the 38 years I have had my Cal 46 with Perkins 4.236 engine. Just past the water intake strainer, I attached a valve and wye fitting, plus a short piece of 3/4" hose with a female hose fitting. This allows me to start the engine on raw water, open the fresh water hose valve and slowly introduce fresh water as I partially close the through hull valve. This allows fresh water to flow through the salt water system w/o excessive pressure. Consider the through hull opening is about 3 feet below the sea surface. So .434 PSI per foot + about 1.5 PSI sea water pressure. Most fresh water systems work at about 65PSI, so be careful.

I also have a short piece of hose on the Tee fitting that allows me to put it into a bucket of chemical mix and/ or anti freeze if I should ever be where it freezes. BRRRR God forbid I should ever go north of Florida.

[greensail]

Hi.

I flush the sea water side of the cooling system every time shut down in the marina.

Having seen the salt and gunge buildup in the heat exchanger I consider it essential, especially it it is difficult to clean.

If it's set up with a fixed system from the fresh water pump, it also provides you with a short term emergency cooling supply if the sea water pump fails. I wouldn't be without it.

Bob