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Old 21-07-2021, 04:53   #1
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Exhaust anti siphon

I have a Yanmar 2gm20 raw water cooled engine which has an anti siphon hose connected between where the water comes out of the engine and where it enters the exhaust elbow. When I start the engine this hose puffs a fair bit of exhaust gas and sometimes a bit of water squirts out. This is annoying because the smell of the exhaust gas isn't too pleasant inside the boat.

This has only occurred since installing a new water-lock muffler and the engine is taking a bit more to get it started than prior. I had to mount the muffler in a slightly different position to the previous one so the exhaust hose to the muffler is slightly longer.

I hope this is not a sign the engine is being harmed with this new set up and any suggestions how to stop the puff of exhaust out of the anti siphon hose would be great.
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Old 21-07-2021, 05:58   #2
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Re: Exhaust anti siphon

Either route the anti siphon hose overboard, or replace the one way valve in the vented loop that is intended to prevent this from occurring.
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Old 21-07-2021, 08:14   #3
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Re: Exhaust anti siphon

Yeah. That little valve on the loop is meant to let air in so it won't siphon, not gases out. Replacing it should solve the problem. It's possible that you have more back pressure in your exhaust than you used to have, which would both load that little valve and make starting a bit more difficult.
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Old 22-07-2021, 10:09   #4
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Re: Exhaust anti siphon

We had a chrome anti siphon loop with a plastic vent screwed in the top it was junk and spewed saltwater every where when it failed. Bought a grocco bronze anti siphon and plumbed the over flow to the bilge. Been 5 years and works flawlessly.
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Old Yesterday, 23:39   #5
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Re: Exhaust anti siphon

Tomodore:

I don't think plumbing the anti-siphon overflow to the bilge is a great idea. When, not if, the lovely Groco anti-siphon valve sticks open, you'll have water and exhaust gases into the boat. Best practice is to plumb the overflow out the side or transom of the boat or into a self draining cockpit. Yes, I heard you say its worked flawlessly for 5 years, but sh_t happens.
Just saying....
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Old Today, 00:19   #6
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Re: Exhaust anti siphon

Quote:
Originally Posted by nuku34 View Post
Tomodore:

I don't think plumbing the anti-siphon overflow to the bilge is a great idea. When, not if, the lovely Groco anti-siphon valve sticks open, you'll have water and exhaust gases into the boat. Best practice is to plumb the overflow out the side or transom of the boat or into a self draining cockpit. Yes, I heard you say its worked flawlessly for 5 years, but sh_t happens.
Just saying....
There is zero chance that exhaust gases will leak into the boat from a correctly installed anti-siphon, and I agree that the best way is a small tube overboard or into the cockpit drain.
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