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Old 23-04-2011, 20:47   #1
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Unhappy Salt Water Cooling Systems

Guys,
I have a 42 foot sloop fitted with an old yanmar YM35 with direct salt water cooling i.e no heat exchanger and have zinc anodes in the block which I replace every 6 months. The 2 inch diameter engine exhaust system has an 'S' propitiatory plastic trap and a 2 ft high (above engine ) anti syphon loop before going out of the hull. Concern I have is do I really need the anti syphon loop as this water must drain back from there via the exhaust system and in so doing pollute the engine if there is an exhaust valve open? Am I correct or missing something?
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Old 23-04-2011, 23:17   #2
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Re: salt water cooling systems

Welcome aboard. My system doesn't need such a siphon loop( fresh water cooling). The loop is usually there to prevent raw water syphoning back into the engine. I am sure there are some on this forum that have more knowledge of your system. Good luck.
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Old 24-04-2011, 02:56   #3
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Re: Salt Water Cooling Systems

All cooling systems need an antisyphon loop in the exhaust to prevent seawater coming back down the exhaust and flooding your engine through an open exhaust valve. You then try to start it and it "hydraulics" ie full of water and busts your pistons

The fresh water cooled engine will have a salt water heat exchanger to cool the circulating fresh water. The saltwater will exit the heat exchanger and be injected into your exhaust manifold and expelled out the exhauist pipe...the water you see out the back of your boat.

Any device that has plumbed in saltwater connections below (or potentially below) the waterline eg salt water flushed head, needs an antisyphon loop either to prevent flooding the device (engine) or your boat !

An d the loops should have one way valves at the top...but check 'em regulalrly to be sure they work..they can get stuck...

My advice ?.....Buy Nigel Calder's excellent book "Boatowners mechanical and Electrical Manual"...it will answer almost any question you have..
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Old 24-04-2011, 07:02   #4
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Re: Salt Water Cooling Systems

Greetings and welcome aboard the CF, John.

See ➥ Yanmar Exhaust Diagram - Cruisers & Sailing Photo Gallery

And ➥ http://www.northern-lights.com/PDFs/...t_drown_me.pdf

And ➥ http://www.yanmarhelp.com/i_exhaust.htm
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Old 24-04-2011, 07:10   #5
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Re: Salt Water Cooling Systems

Quote:
Concern I have is do I really need the anti syphon loop as this water must drain back from there via the exhaust system and in so doing pollute the engine if there is an exhaust valve open? Am I correct or missing something
The cooling water will be injected into the "downhill" side of your exhaust pipe riser. The riser in the exhaust pipe needs to be higher than the waterline at all angles of heel in order to prevent water backing up the exhaust pipe into the engine. The anti-siphon valve in the top of the water injection line is there to prevent water from siphoning back into the engine through the cooling water line. There are good diagrams in Nigel Calder's Boat Owners Mechanical and Electrical Manual.

When I had to have part of my exhaust system rebuilt in Panama a clever mechanic there connected the anti-siphon line to a small tee fitting in a cockpit drain that is near the helm station. The cockpit drain opens to the air in the cockpit, so it prevents a siphon and I can hear the water running into the drain when the engine is running, giving me an audible confirmation that my engine is pumping water. Plus, I don't have a finicky anti-siphon valve to worry about--they frequently clog up with salt.
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