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Old 13-10-2017, 11:14   #16
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Re: Yanmar Fresh Water Thermostat

.32 caliber, cut off rifle shaft extension, and a battery powered drill. I don't even take off the back cap after the first time.
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Old 13-10-2017, 11:17   #17
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Re: Yanmar Fresh Water Thermostat

You're kidding! That's all it takes? I've got a couple of those.
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Old 13-10-2017, 17:11   #18
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Re: Yanmar Fresh Water Thermostat

I've been in many engine factories. Most OEMs only make the basic parts, not thermostats, etc. most small parts are made by a specialty company. Usually aftermarket parts are made by the same specialty company and just put in a different box. Years ago I got an unauthorized tour of a bearing maker. On a line making shell bearings for a major diesel maker, I saw the switch over and the only difference was a different box (but a major bearing brand) suddenly began taking the finished bearings.
For my Detroits, I can pay $100 for a DD thermostat or $25 for an aftermarket. Never had an aftermarket fail and they look the same. Same for bearings, seals, engine kit and so on.
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Old 13-10-2017, 18:46   #19
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Re: Yanmar Fresh Water Thermostat

Hi
I have a 3JH and after alot of research I could not get the correct temperature range. As they were all for auto and plant use they were all about 10-20 degrees too hot. I think mine opened by 78 degrees C.

I had to go genuine and have toast for dinner....

Cheers Tom
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Old 13-10-2017, 19:04   #20
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Re: Yanmar Fresh Water Thermostat

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I took off the heat exchanger's forward end cap, where the raw water enters. There was a little sediment and a small piece of shell at the bottom, but above the lowest row of tubes it appeared quite clean. I intend to get a tube brush once I've measured the diameter of those and make sure, but I don't think that's an issue.
The best way to clean a tube stack is to remove it, Put it into a pvc pipe that is capped on one end and soak it in white vinegar (a mild acid) overnight. Flush it and put it back in service.

You will need to partially drain your antifreeze to prevent it from pouring out when you remove the tube stack. You will probably need new O rings or whatever scheme Yanmar uses to seal the stack ends.
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Old 13-10-2017, 20:55   #21
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Re: Yanmar Fresh Water Thermostat

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My new old sailboat Sequoyah has a 1999 Yanmar 3GM30F with a Y/M thermostat no. 121750-49800 in the fresh water cooling system. It's old, and I suspect tired, so in a fresh (so to speak) start I'd like to replace it.

The genuine Yanmar part is the price of a good dinner out, and if possible I'd rather eat well than stick needlessly with OEM parts. Does anyone know of a more reasonably priced substitute for this thermostat?
Actually, Yanmar parts are quite reasonable compared to other marine diesel manufacturers. I recommend supporting the manufacturer, so they stay in business so we will have great reliable marine engines in the future. (I am a Yanmar dealer.)
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Old 14-10-2017, 03:00   #22
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Re: Yanmar Fresh Water Thermostat

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Actually, Yanmar parts are quite reasonable compared to other marine diesel manufacturers. I recommend supporting the manufacturer, so they stay in business so we will have great reliable marine engines in the future. (I am a Yanmar dealer.)
Having owned and managed a small manufacturing plant in a past life, ramblinrod, I can appreciate that. In this life fortunately or not I'm a poor sailor and need to save dollars where I can. Whether or not I can do it in this instance remains to be seen, but I'll let you know here once I've tried. Thanks for the comment.
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Old 14-10-2017, 03:02   #23
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Re: Yanmar Fresh Water Thermostat

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The best way to clean a tube stack is to remove it, Put it into a pvc pipe that is capped on one end and soak it in white vinegar (a mild acid) overnight. Flush it and put it back in service.

You will need to partially drain your antifreeze to prevent it from pouring out when you remove the tube stack. You will probably need new O rings or whatever scheme Yanmar uses to seal the stack ends.
Mine doesn't look like it needs a thorough cleaning, stormalong. Good tip, though. I'll make a note of it in my maintenance log. No doubt it'll be useful along the way.
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Old 14-10-2017, 03:07   #24
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Re: Yanmar Fresh Water Thermostat

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Mine doesn't look like it needs a thorough cleaning, stormalong. Good tip, though. I'll make a note of it in my maintenance log. No doubt it'll be useful along the way.
You would be surprised how much buildup accumulates. I just did my engine with about 4000 hours on it. It made a considerable difference in cooling.
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Old 14-10-2017, 03:07   #25
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Re: Yanmar Fresh Water Thermostat

[QUOTE=Nineteen;2498763]Hi
I have a 3JH and after alot of research I could not get the correct temperature range. As they were all for auto and plant use they were all about 10-20 degrees too hot. I think mine opened by 78 degrees C.

I had to go genuine and have toast for dinner....

Heheh ... I'm starting to suspect I'll have to do that in the end, Tom. I'm not yet done trying to be cheap, though. I do intend to put a cooking thermometer into the pot when I give the old thermostat a boil test so I'll know at what temperature it opens, if it does atall.
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Old 14-10-2017, 03:09   #26
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Re: Yanmar Fresh Water Thermostat

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You would be surprised how much buildup accumulates. I just did my engine with about 4000 hours on it. It made a considerable difference in cooling.
My motor has only 300 hours. I guess I'll know more about the tubes' condition once I remove the end caps, shine a light down them, and run a brush through.
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Old 14-10-2017, 14:00   #27
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Re: Yanmar Fresh Water Thermostat

Keep looking for a generic replacement. I found by looking at parts suppliers for all the engines in the same series I eventually found a cross reference or specs. You will find many of the thermostats from the same era are the same. Opening temperature is often marked on the part. Go to good auto parts store with the thermostat in hand.
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Old 14-10-2017, 14:47   #28
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Re: Yanmar Fresh Water Thermostat

I do intend to search for it, but first I want to take a set of measurements from it to record in my maintenance log.

What is a typical opening temperature rating for small inboard diesels, by the way, or more specifically for a Yanmar 30GH30F? Anyone know?
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Old 14-10-2017, 14:53   #29
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Re: Yanmar Fresh Water Thermostat

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The best way to clean a tube stack is to remove it, Put it into a pvc pipe that is capped on one end and soak it in white vinegar (a mild acid) overnight. Flush it and put it back in service.

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.
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Old 14-10-2017, 15:06   #30
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Re: Yanmar Fresh Water Thermostat

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?
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