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Old 14-10-2017, 18:24   #31
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Re: Yanmar Fresh Water Thermostat

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Originally Posted by a64pilot View Post
Be careful with that, I pulled the one out of my 4JHE and put it in a Lowe’s bucket with some acid and it started boiling like crazy, very soon I realized no way was there that much calcium so I pulled it out, got a good look at it and realized it was either heavily plated with zinc, or many of the parts were zinc.
Acid, even vinegar will destroy zinc in a hurry.
So will sea water. If your tube stack was made with zinc the maker should be avoided at all cost. Tube stacks should be made with cupro-nickel alloy. Brass is a copper-zinc alloy, bronze is copper-tin. That is why yout sea cocks may by bronze but must not be brass.

What acid were you using?
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Old 14-10-2017, 18:55   #32
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Re: Yanmar Fresh Water Thermostat

I have a 2GM (owned for 20years) and a 3GM (owned for 12 years). I have kept the sea water side of the heat exchangers cleaned with the pistol cleaning brush/ drill since day one. A boat yard manager in the Keys told me to pull the tube bank and use a mild acid. Decided to try a different approach and never looked back. First time I pulled both end caps, now don't even bother with the back one. One gasket, 20 minutes and done.

If you haven't noticed the sea water side is a three pass path set up. Don't have the foggiest idea what the tube material is but copper nickel would be a good bet.
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Old 14-10-2017, 19:32   #33
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Re: Yanmar Fresh Water Thermostat

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Noted, and thanks. Why do they make them that way? Is it perhaps a substitute for sacrificial anodes on motors that don't have them by design?


That is my theory, as my old 4JHE does not have a sacrificial anode.
Seems foolish for it not to, but just maybe average Joe boater doesn’t know what a sacrificial anode is, so they don’t get changed, and Yanmar tried to outsmart them?
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Old 14-10-2017, 19:46   #34
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Re: Yanmar Fresh Water Thermostat

Yanmar typically uses cupro-nickel alloy for their heat exchangers and this metal does not require zinc for protection.
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Old 20-10-2017, 13:52   #35
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Re: Yanmar Fresh Water Thermostat

So why do every one want to grind off the cupro nickel off ?
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Old 20-10-2017, 14:15   #36
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Re: Yanmar Fresh Water Thermostat

I have the old thermostat out, Yanmar part no. 121750-49800 (I assume). Here is the stamping from its flange:
71 degrees C
A logo, a capital A with the letters FT below the bar
Two numbers: 97 and 12

It is not a dual. It has one valve disc at the top, and another, smaller disc at the bottom not sealed that must be a tensioning device rather than a valve.

Over height is 61mm, height from flange to base 42mm
Flange diameter: 44mm
Lower disc diameter: 28mm
Diameter of dome housing above flange: 30.5mm
Diameter of open frame below flange: 37mm

A stove pot test opened the valve starting at 160F, just as the stamped temperature rating calls for. The valve was fully open at 180F. I conclude from this that it is working properly and does not need to be replaced.

I nonetheless carried it around to some parts places. Two of them told me this same engine is used in a common front end loader. Only one shop, a diesel engine dealership, could quote me on it at all. It would charge about half the price of the marine dealers with whom I have spoken and would have to order it in.

I tried again to find a substitute on the Internet. Dayco, referenced in a post above, lists no match. Stant too appears not to have one. I could uncover no cross reference using the Yanmar part number.

Conclusion:
A. Success with the basic problem: the old thermostat is still good.
B. Failure on finding a generic replacement.
c. Partial success on getting the price down somewhat: a tractor dealer may provide it for less than a chandlery.
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Old 20-10-2017, 18:27   #37
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Re: Yanmar Fresh Water Thermostat

Sounds like a win👍
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