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Old 22-11-2017, 18:09   #1
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Exhaust Plumbing Bypass Stern Squirt

I finally decided to replace my mixing elbow and noticed some curious plumbing. Please see image below.

It appears that there is a cooling water detour before reaching the mixing elbow. This little detour exits the boat just above the main exhaust.

Does anyone know the reason to route some of the water overboard before the mixing elbow?

I think the prior owner explain it was a way to see that the cooling water was flowing without having to look over the stern since it exits the boat in a thin squirting stream visible from the cockpit. (I donít think he did the plumbing)

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Old 22-11-2017, 18:30   #2
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Re: Exhaust Plumbing Bypass Stern Squirt

My guess would be that small stream is from the vented loop or anti-siphon valve instead of a small rubber duckbill. Guarantees that the valve never stays closed
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Old 22-11-2017, 20:30   #3
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Re: Exhaust Plumbing Bypass Stern Squirt

It is the anti siphon. Very important. Should be very small stream.
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Old 22-11-2017, 22:42   #4
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Re: Exhaust Plumbing Bypass Stern Squirt

It's a good way of doing it. The little valves often get salted up which can cause a hydro lock, by having a small tube instead of a valve there is very little chance of a blockage, also you can visually see that it's ok,if waters coming out, you are right to go.
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Old 22-11-2017, 23:49   #5
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Re: Exhaust Plumbing Bypass Stern Squirt

Ok, I see. Iím used to seeing the little duckbill like the head intake has.
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Old 23-11-2017, 08:18   #6
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Re: Exhaust Plumbing Bypass Stern Squirt

It is also used to reduce exhaust system back pressure. Some lift mufflers, if they must lift some distance, create back pressure that is above the engine manufacturers spec. Bypassing part of the cooling water reduces this.
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Old 23-11-2017, 08:22   #7
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Re: Exhaust Plumbing Bypass Stern Squirt

Quote:
Originally Posted by Mojadito View Post
It is also used to reduce exhaust system back pressure. Some lift mufflers, if they must lift some distance, create back pressure that is above the engine manufacturers spec. Bypassing part of the cooling water reduces this.
I don't understand this? How does water exiting through the exhaust create back pressure? replacing space that could be used for exhaust gas? Sorry, don't get it, no criticism.
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Old 23-11-2017, 08:27   #8
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Re: Exhaust Plumbing Bypass Stern Squirt

Quote:
Originally Posted by daletournier View Post
It's a good way of doing it. The little valves often get salted up which can cause a hydro lock, by having a small tube instead of a valve there is very little chance of a blockage, also you can visually see that it's ok,if waters coming out, you are right to go.
This is the good way to do it. No spring, no plastic piston to seize. When needed, flush with fresh.

Or think differently and dispose of the anti-siphon completely.
http://www.cruisersforum.com/attachm...xhaust-med.jpg
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Old 23-11-2017, 08:35   #9
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Re: Exhaust Plumbing Bypass Stern Squirt

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Originally Posted by S/V Alchemy View Post
This is the good way to do it. No spring, no plastic piston to seize. When needed, flush with fresh.

Or think differently and dispose of the anti-siphon completely.
http://www.cruisersforum.com/attachm...xhaust-med.jpg
Never seen this, but great idea if boat design enables you to do it. Impossible to siphon back.
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Old 23-11-2017, 08:45   #10
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Re: Exhaust Plumbing Bypass Stern Squirt

Iíve also seen a muffler setup where the muffler is essentially an air water seperator. I donít recall details ATM. our big boat has an exceptional Loooong exhaust run and I keep trying to come up with alternatives.
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Old 23-11-2017, 10:33   #11
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Re: Exhaust Plumbing Bypass Stern Squirt

I just replaced the mixing elbow on a yanmar 3gm which had the same setup, exhaust water from heat exchange had a T to allow water to go to the mixing elbow and a another hose that sent it overboard. do not think it is a anti siphon valve. maybe a safety to prevent engine from overheating in case the mixing elbow gets clogged which this did. Just thinking here. this was the fist one that I came across that had this setup.
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Old 23-11-2017, 12:49   #12
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Its the anti syphon - I have the same on my boat. As previous posters have said, it saves worrying about salt deposits seizing up an anti-syphon valve.
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Old 23-11-2017, 13:00   #13
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Re: Exhaust Plumbing Bypass Stern Squirt

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Originally Posted by boeing1 View Post
I just replaced the mixing elbow on a yanmar 3gm which had the same setup, exhaust water from heat exchange had a T to allow water to go to the mixing elbow and a another hose that sent it overboard. do not think it is a anti siphon valve. maybe a safety to prevent engine from overheating in case the mixing elbow gets clogged which this did. Just thinking here. this was the fist one that I came across that had this setup.
No, that was an anti-siphon.
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Old 23-11-2017, 17:05   #14
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Re: Exhaust Plumbing Bypass Stern Squirt

Quote:
Originally Posted by boeing1 View Post
I just replaced the mixing elbow on a yanmar 3gm which had the same setup, exhaust water from heat exchange had a T to allow water to go to the mixing elbow and a another hose that sent it overboard. do not think it is a anti siphon valve. maybe a safety to prevent engine from overheating in case the mixing elbow gets clogged which this did. Just thinking here. this was the fist one that I came across that had this setup.


Interesting, I have a 3gm30...
But it definitely seems like the anti siphon. The Yanmar services manual doesnít show it in its diagram, but the E&M manual shows it.

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Old 23-11-2017, 20:17   #15
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Exhaust Plumbing Bypass Stern Squirt

UPDATE: After replacing the mixing elbow the vale/siphon no longer squirts water at idle, and doesnít shoot as far at higher rpms. My guess is that the elbow was so clogged that it was backing up and out the siphon. Now I wish I had a video for comparison and illustration/reference purposes.

I would post a pic of the old elbow but it looks just like all the other corroded ones on the web
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