MS 390 - Add fresh water flush to raw water intake

[Lshulan]

my new to me MS 390 2002 with Yanmar 6lya-stp 370hp has the typical raw water strainer between thru hull and raw water pump. This boat had previously only been in fresh water (other than 1 year) and I'd like to keep it that way as much as possible. So adding a fresh water rinse would be a large improvement. Have any of you added a fresh water rinse option to the raw water system? I understand that there are several ways to do this, one is to change the top of the raw water strainer bucket to one with a quick connect for garden hose and a shut off valve. I'd like to do this myself as this would seem to be very simple and reliable. I don't want to try to mess with the hoses, they look like I'd be cursing and bleeding by the time I was done and I'm looking for simple. Any ideas would be appreciated. If you have any details (such as brand and model numbers, specs, etc) even more appreciated.

 

[DavidM]

This is what I did, see the pic. The top was drilled and tapped for a 3/8" NPT street ell, valve and hose fitting.

David

 

[Lshulan]

David - that looks great and simple. Couple of questions: if planning on using 1/2” garden hose, would there be any reason not to use 1/2” ell and associated parts? Does the fresh water “keep up” with the raw water pump? Any words of caution in this?

Thanks for quick response.

 

[lipets]

I assume you close the main saltwater valve first


May even use Barnacle buster right into when needed?

 

[Lshulan]

David - one other question, is the lid of the strainer bronze? if so, what material is the street ell made of, wondering about galvanic corrosion issues?

 

[Comodave]

Just use a bronze ell. You can get them but make sure it is actually bronze not brass.

 

[Chuck34]

This is what I did, see the pic. The top was drilled and tapped for a 3/8" NPT street ell, valve and hose fitting.

David

I have the exact same set up on my Perko strainers. I have them on both engines, my genset and my AC water line. Not only good for flushing but makes winterizing a breeze. I also have a 3 gallon bucket with a faucet tapped into the bottom and a short 4-5’ hose to connect to the strainers. Fill up the bucket with anti freeze, turn on the engine and suck the AF in. Done.

 

[DennisB1]

I have a set up using a groco connector to a tee in the raw water line. Process is to hook up the hose to the Quick connect start the engine at idle with thru hull open. Then close the thru hull and open the fresh water supply at about the same time. Run engine for about 5 minutes to flush engine. The Shut off fresh water then stop engine (within a few seconds. The fresh water is a pressure line so it is shut off first. The FW hose does not supply as much as needed for my engine so the pressure goes negative (below ambient pressure)(cat 3208TA 1-1/4 Jabsco pump) the water flow is sufficient to lubricate the impeller so no issues with destroying the impeller (dry running). The hose flows about 5 gpm. Smaller engines could have a positive pressure so a different procedure may be required to not over pressurize the seals on the raw water pump. I flush the engine for storage or for changing the pencil sinks in the heat exchangers.

 

[Comodave]

We have a SeaFlush that we used to use for winterizing. It plugs into the top of the strainer with the basket removed. Then you draw antifreeze or water in from a 5 gallon bucket. That way there isn’t starvation or over pressuring the engine.

 

[Shrew]

I use one on my AC intake for winterization purposes.

https://www.defender.com/product.jsp?path=-1|2285701|3014947&id=2755962

 

[Lshulan]

Fresh water flushing

That’s a great idea, can accomplish two things with one product. How much hassle was it removing existing hose and reattaching? The size of my hose and the fact it’s been on for 20 years gives me heartburn thinking of it.

 

[DavidM]

Lshulan:

Sorry I missed your earlier posts and questions.

Yes the lid to my Perko strainer is bronze and the street ell and the Appolo valve is bronze. The hose connector is brass, but since it is always in fresh water, ie it is upstream of the valve, no problem with corrosion.

On my dock with low water pressure, the raw water pump even at idle would pull more water than the dock hose would provide and partially collapse it. Here is how you operate it:

Close the raw water thru hull valve and connect a hose to the hose fitting. Start the engine. Starting the engine first is important as you don't want to pressurize the raw water pump and blow out its seal. Then quickly turn on the dock water and let it run for 3-4 minutes to flush out the sea water. Then turn off the dock water and quickly kill the engine. Running the engine for 5-10 seconds with no water flow won't hurt anything.

David

 

[Lshulan]

Fresh water flush

DavidM - thanks for the update. So basically you have some raw water mixed with the fresh, is that right? I have pretty good water pressure at my dock and was going to go with a half inch setup using a 3/4” heavy duty hose from my dock. So perhaps I could get away with either all fresh or by just partially closing thru hull, a stronger fresh to raw mix making sure the hose doesn’t collapse. Also, is the lid of the strainer thick enough so that when threaded, there’s enough of the bronze (which isn’t the strongest metal I believe) threaded part to hold the valve assembly if it were accidentally kicked or something fell up against it without allowing for any leaks? I ask because if I remember from something I read that thru hulls and connections must be robust enough to withstand being moved or bent in the event of something accidentally hitting it such as being kicked.

 

[DavidM]

I did not mix fresh with salt water. I fully closed off the raw water thruhull valve and relied on the dock fresh water pressure to flush the engine. No, it doesn't get as much fresh as salt water with the low dock water pressure I have, but it is enough to lubricate the raw water pump and keep the engine cool while it pushes out the salt water.

David

 

[Lshulan]

DavidM - my mistake, I apologize. I didn’t read your post accurately, when re-reading, it’s clear that you aren’t mixing fresh and raw. Sorry. Thanks for the info, over the winter I will make this modification and then next year, will be doing fresh water rinses extending the life of the engine.

 

[dhays]

I do what David does only I first turn on the dock water with the raw water seacock open. This then causes fresh water to backflow out the seacock. Then I start the engine and then close the seacock. Run 5-10 minutes then shut off the water and engine. I have a **** off valve in the hose I use that is right at hand so there is only a few seconds between shutting off the water and shutting down the engine.

Then open the seacock.

 

[Lshulan]

Dhays - that looks like a great way to perform the rinse and I like the idea of the shut off on the hose Thanks

 

[firehoser75]

DavidM and DHays have it right. Do not have dock water under pressure going into the engine when it is not running!!
I did it like DHays. Open seacock. Turn on dockwater. Start engine. Shut seacock and run engine for about 5 minutes to flush. Shutdown dock water (for me at the seacock), and as quickly as possible shutdown engine. Open seacock to remove any pressure after ensuring the dock spiggot is off. If you are worried about your dock water not supplying enough water, you can leave the seacock open a bit to mix in seawater. Even this is much better than leaving things full of seawater, but most dock supplies are adequate. I also used a fairly "stiff" hose to keep it from being partially collapsed by the engine draw. My freshwater connection was through the strainer lid as well. Marine age is what "kills" engines (at least one of the things), and this occurs even when not running if salt water is left sitting in the system.
Freshwater flushing is well worth the small amount of time and effort involved!!

 

[Shrew]

How much hassle was it removing existing hose and reattaching? The size of my hose and the fact it’s been on for 20 years gives me heartburn thinking of it.

No hose should be 20 years old. Don't worry about how hard it is to remove. The best thing you can do is cut it off (which makes removal simple) then replace it with a new hose.

On that note, I would assume all the hoses are old and start replacing all of them. Like the one that is between the seacock and the sea strainer for the engine that many people either skip over or forget about.

When I went to replace the hose from my sea strainer to the seacock it tore (shredded) in my hands when I attempted to remove it. I then replaced all raw water intake and exhaust hoses and inspected all the other hoses.

 

[Bonedoc]

a few thoughts....

1. Shrew beat me to it. Change out your hoses and belts as an untimely catastrophe may be lurking!

2. Many with more experience than myself recommend NOT closing your raw water seacock as there may be that one time when you forget to reopen it and you fry your expensive motor before you have a chance to respond. Obviously a full fresh water flush is the ideal, but a flush with the seacock open would accomplish the majority of what you are looking for without the risk due to the higher pressure of the hose water running at idle.

 

[Lucie]

I just fitted this system in Australia
https://aditmarine.com.au/

Easy to fit and so easy to use.

 

[Sailinggod]

Be careful to leave your raw water through hull open when you flush with fresh water, as the hose will not provide enough water to keep the engine cool. You will get mostly fresh and this will help flush salt water out of your cooling system and keep it lower maintenance. Although I haven’t done it, I’ve seen it done on other boats and of course they swear by it. Although they put a fitting in the hose line, not drilled into the raw water strainer. Proper fittings would be the way to go, ensuring you use brass, not plastic, as that would not pass a survey.

 

[Lucie]

Be careful to leave your raw water through hull open when you flush with fresh water, as the hose will not provide enough water to keep the engine cool. You will get mostly fresh and this will help flush salt water out of your cooling system and keep it lower maintenance. Although I haven’t done it, I’ve seen it done on other boats and of course they swear by it. Although they put a fitting in the hose line, not drilled into the raw water strainer. Proper fittings would be the way to go, ensuring you use brass, not plastic, as that would not pass a survey.

Yep. It's all part of the system. Through hull is to be open when flushing. I removed the heat exchanger after the last flush and the water was fresh.

 

[Xlantic]

Here is an Seaboard Marine video on fresh water flushing (you can skip the first 2 minutes):

https://www.sbmar.com/video-gallery-how-to/

They recommend leaving the sea-cock open throughout.

 

[Marty4]

Here is an Seaboard Marine video on fresh water flushing (you can skip the first 2 minutes):

https://www.sbmar.com/video-gallery-how-to/

They recommend leaving the sea-cock open throughout.

Lots of ways to do it as the video points out. Find one that you are comfortable with.

On my little VP-D1-30 I use the one discussed near the end of the video. I added a 2-3ft section of hose that I Tee'd into the suction side of the strainer that I leave in place capped off. I flush after every use and just stick the garden hose and my short suction hose in a bucket. Fill the bucket, turn off the sea cock and fire up the engine. The engine will suck at the rate it wants based on the RPM you run at and will never overheat as long as the level in bucket is above the suction hose. Cap the short suction hose and open the seacock when done. I use the same bucket method to add Barnacle Buster for a cleaning or add antifreeze if I want to winterize the system.

 

[Greg QS]

I always try to make flushing as simple as possible. If not you may not use it all the time. I tied my engines into the fresh water system. I am plugged in after the raw water pump. I simply go into the engine room and flip a valve. Engine does not need to run.. I let it run for 10 min or so. Sometimes it backflows into the sea strainer, sometimes not. When doing this approach you need to confirm you have a high rise exhaust and there is no way to back drain into the engine. Example this approach will not work with lift mufflers. This is also my winterization system. While i have antifreeze in my water system, i just flip a valve and wait for pink out the exhaust. Done.

 

[lwarden]

Couple of things to consider with this which was discussed in another thread.
I added fresh water flushing a couple years ago and did the open seacock method for a year. I found that even with good water pressure I still had significant salinity in the water when sampled. Also, I was surprised to see that zinc wear was similar to when I didn't flush. So, I'm going to switch to closing the seacock as described above and pray I don't forget to open them once done. There is plenty of water coming through the hose to cool an idling engine so should be no issue there. The only problem would be that the shower at the mixer may not be fully filled and could lead to hot spots downstream. I will monitor that but again at idle don't see an issue happening.