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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


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Old 01-13-2013
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old yanmar 12hp RW single

I have a few basic questions regarding an older yanmar RW single 12hp, I believe it is mid seventies. I found a small leak, or what I thought was a leak coming from the water discharge line out of the top of the head, clamped onto a ss inverted U pipe with a teflon double-screen threaded onto a 1/4" nipple at the top of the inverted U...The other line at the fore end of U pipe discharges into the vertical exhaust manifold...I am thinking this is some kind of after market vacuum lock prevention? I originally thought it was a pressure release valve, but after dis-assembly, it is not... water and or air may pass either direction. It is mounted at the upper rear of engine compartment, and appears to drip from the teflon screens ... Questions: Is this 'telon breather' what i stated? (after market anti-vacuum lock etc.) if it is, should it be drip leaking ? At first I thought it was the lines, as they were sloppily installed and badly chaffed in two places ( needed to be replaced anyhow) but my question also is, can I remove the teflon breather, add a flexible line and relocate the dripping to a more suitable location. ANY help with this would be great...thanks for any info ...meanwhile, I continue to seek out local old yanmar guru...
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Old 01-13-2013
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Re: old yanmar 12hp RW single

Ben,

I've been trying to draw a mental picture of your situation -- hopefully I've got it right.

The inverted "U" device you describe is probably an anti-siphon loop. Its purpose is to make sure that your r/w cooling circuit cannot back-flow through the exhaust manifold and flood your cylinders. You need one of these, so repair or replace are the two options.

The teflon screen sounds like the one-way valve which is normally installed at the top of the inverted U. When water is flowing through the system, the pressure inside the loop should close the valve; once you shut down the engine, the pressure goes to zero and the valve opens allowing water to drop back to sea level. You can test the valve by blowing & sucking on the threaded end; you should not be able to blow air out, but you should be able to suck air in.

The one way valves are often the point of failure of the anti-siphon loop. When they do fail, the results are pretty much as you describe -- leaking water from the top of the loop. Sometimes they accumulate salt/calcium crystals that keeps the flapper valve from closing completely -- try soaking the valve in vinegar to see if that restores the proper function. If that doesn't work, try to find a replacement valve. Failing that, you can replace the entire loop (the inverted U together with the one-way valve.)
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Old 01-14-2013
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Re: old yanmar 12hp RW single

Pro-Fin,
Thanks much for the guidance...I believe you have the proper name...'anti-siphon' and I believe it to be doing just what you have described...although I am not certain that the correct anti-siphon device was installed with my unit...I have discovered much sloppy recent work as I have been going through the vessel, this may be another case. my question is what is the technical name of the teflon part, and where do I find a new one? They can't be that expensive, and I really don't see any valve in this unit...it appears to have been leaking for the year's worth of time it has been installed...the ss U pipe is like new also... Thanks again for the help...this is an old Irwin 30, and is my first what I consider 'big' boat & diesel...she sails great and have been bringing her back to life bit by bit. Eventually I will need to find I-30 folks of that era that have up-graded their power plants, 12 hp is fine for it's past racing days and or my day sailing....but some what scary for serious coast cursing.
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Old 01-14-2013
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Re: old yanmar 12hp RW single

Now there's the challenge -- finding a replacement valve.

OK, the easiest way is to just replace the whole thing. Notice I said easiest, not cheapest. Most decent marine stores carry them, and can be found as "vented loops," "siphon break" or "anti-siphon valve." Match the replacement to your water hose size, pay the man, and off you go. You can usually find them in either Marelon or bronze.

Now moving up the effort-expended scale, you get to finding a replacement valve for your stainless piece. If you are living right, one of these will work (all you need is the "vacuum breaker" part):

Clicky

If not, then mining the internet for other options may yield results.

A less elegant solution is to build your own loop using plumbing supplies.

Best of luck.
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Re: old yanmar 12hp RW single

That is it...Thanks for all the help...happy sails!
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