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Old 12-06-2017, 07:48   #1
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Flushing raw water system

Just curious as to how often does everyone flush their raw water system, and what method works best. Was thinking of adding a tee fitting with a hose attachement to facilitate. Also is there a flushing solution or is fresh water good enough.

Thanks in advance!
Will
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Old 12-06-2017, 08:17   #2
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Re: Flushing raw water system

On the engine?

Never.

When we'll be away from the boat for more than a few days though we do run fresh through the head and wash down pump.
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Old 13-06-2017, 23:43   #3
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Re: Flushing raw water system

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Originally Posted by Clipper4730 View Post
Just curious as to how often does everyone flush their raw water system, and what method works best. Was thinking of adding a tee fitting with a hose attachement to facilitate. Also is there a flushing solution or is fresh water good enough.
1. How often to flush?

I do not think there is one universal answer.

Depends on the nature of the water that floats your boat, how frequently you use your engine, air and water temperature, the metals and electropotentials of your engine and prop shaft, and more.

If you use your engine and prop at least once a week, you a less likely to have problems with calcium deposits accumulating in a heat exchanger or in the shaft log (on the shaft in the cutless bearing, in the shaft seal) than if you only use your engine and prop once a month.

Some seawater is more calcium rich than other seawater. Biological activity and the chemistry of the water differ by temperature and location. And if your prop shaft is well protected by zinc or aluminium anodes, the shaft might be more prone to having calcium deposits accumulate on it.

Tropical and some temperate sea water seem quite prone to calcium deposits in the heat exchanger and on the shaft where it is especially noticed in the shaft seal and the cutless bearing. Significant calcium deposits on the shaft form after seawater has sat in the shaft log for just over one week in tropical and warm temperate waters.

If you have a packless/dripless shaft seal, such as the PYI PSS I have installed on Led Myne, you can notice the deposits if you rotate your prop shaft by hand. If I rotate the shaft one week after the last use of the engine, the shaft turns without resistance. Any longer than one week and some resistance is detectable. If I just turn on the engine, the rubber bellows of the PSS is lightly stressed until the calcium deposit the stiction it causes are broken. That's one of the reasons that those rubber bellows need to be replaced regularly.

Same goes for the cutless bearing. If you motor every week in clean (not turbid or gritty) water, a cutless bearing can last a decade or longer. If you only motor once a month, the rubber staves of the cutless bearing have to brush away the calcium deposit. That abrasion might reduce the life of your cutless bearing to about 3 years.

If you have an engine, such as the Yanmar on Led Myne, with a cast iron exhaust mixing elbow, you'll know that Yanmar regards it as a consummable item. That's because it is prone both to rust and calcium deposits clogging its water channel. Use the engine every week and an exhaust mixing elbow lasts for years. Use the same engine only once a month, without flushing it with freshwater, and an exhaust mixing elbow only lasts 3 years. I know that by experience.

I keep Led Myne in a marina. Each time I return to the marina, I flush the engine at idle. In Led Myne's case, some of whatever water picked up by the raw water impeller pump is also injected into the shaft log at the PYI PSS.


2. What method works well?

A 20 litre (5 US gallons) pail, with a length of hose feeding water from that pail into a T-piece (such as a Quick Flush Valve. See: How it works - Quick Flush Valve System - boat engine flushing, winterizing and emergency bilge pump kit, Gas, Diesel, Out Drive Marine Engines, Generators, AC units and look at the sort of equipment sold at that website)

3. Is fresh water good enough?

To avoid leaving the engine and shaft log soaking in saltwater and if you have a regular flushing schedule, the answer is probably yes.

If your engine has an internal zinc anode, you might want to research what happens to zinc anodes in freshwater.

Of course, you might want to add antifreeze solution to the flush water if you expect air temps falling below the freezing point of water.

The marketplace has a range of proprietary flushing additives that claim to eliminate salt and calcium deposits. I've not use them so I cannot comment.
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Old 14-06-2017, 03:34   #4
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Re: Flushing raw water system

We gave ours a nice fresh water flush while transiting the Panama Canal. Otherwise I have never even considered it.

We have a freshwater cooled Yanmar 4JH3.

Steve
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Old 14-06-2017, 04:11   #5
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Re: Flushing raw water system

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Originally Posted by Clipper4730 View Post
Just curious as to how often does everyone flush their raw water system, and what method works best. Was thinking of adding a tee fitting with a hose attachement to facilitate. Also is there a flushing solution or is fresh water good enough.

Thanks in advance!
Will
We have flushed raw water systems -- engines, genset, ACs -- with Rydlyme and with Barnacle Buster; both seem equally effective, although they're each a different diluted acid solution... so it might pay to match acid with whatever system you're doing.

I've used both a recirculating method and a fill-soak-flush method; former maybe works slightly better but takes a bit more effort. OTOH, making up several hoses and fittings then means those are reusable, and a small transfer pump often comes in handy for other things, too...

I've only had to do engines and genset once, so far. Fresh water flush, more often, wouldn't hurt, but we're in brackish water so don't get full salt build-up like some would do.

OTOH, the AC systems need flushing more often, probably twice year.

The flush attachment is also useful for winterizing, if you have to do that...

-Chris
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Old 18-06-2017, 11:33   #6
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Re: Flushing raw water system

As was mentioned earlier, you should have a fair understanding of the metals used in your engine's raw water system. I have flushed heat exchangers on the engine and off. I've come to respect Mercedes Benz's citric acid flushing chemistry the most. When I've cleaned heat exchangers off the boat and can visually watch the process, a 10% by weight solution of citric acid and water does an excellent job but takes a bit longer. Both Barnacle Buster and Rydlyme are more aggressive to the metals and can be seen to remove more surface metal.

On the engine, reverse recirculation works the best. A cheap bilge pump in a 5 gal bucket works fine. Take the impeller out of your raw water pump and wrap an old nylon stocking around the bilge pump to filter out the chunks. Bilge pump outlet to exhaust manifold outlet and inlet water strainer hose to bucket. Recirculate for 3 hours or so.

Ken
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