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Discussion Starter · #1 · (Edited)
(There is no) Zinc pencil on Yanmar 3GM30F

Hello,

I have a Yanmar 3GM30F in my boat, and the manual says I should replace the zinc pencil at last yearly. The manual states that the pencil is labeled with the words 'anti corrosion zinc', but I have looked all over the darn heat exchanger and can't find the thing (maybe the label sticker fell off?) -- the manual doesn't have a diagram pointing to it either.

Can anyone who owns a 3GM30F explain where the zinc pencil is, or send a picture showing me where to look! I can't bear the thought of my poor engine corroding, but I don't want to start randomly removing bolts looking for the thing...

Regards,

--
Joe
 

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I have a Yanmar 3GMD with the same exact zonc setup. I am due to replace mine very soon...just waiting till spring commisioning time so I don't have to re-winterize the motor after flushing the cooling system to change the zincs.

Let me know how it goes when you change them and if there is anything I should know. One thing I noticed is the bolt for the zinc on the left side of the motor is almost impossible to get to as there is a fuel line or something right in front of it. Should be fun...
 

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Warm Weather Sailor
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They no longer put zincs in the 3GM30F but at the rear of the motor, above the transmission, you will see a plate where the zinc used to go. I have had mine since the early nineties and no problems. I too wondered about it as the manual does indicate zincs but Yanmar claims they're so good they don't need them. At least this is what the dealer told me.
 

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I will have to check. But I was told by several sources that there are NO zincs on the F model. Any other yanmar owners, what do you have?
 

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Learning the HARD way...
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My Yanmar 2QM15 has 2 zincs one near the transmission and one in front. But my engine is raw water cooler. For fresh water cooler engine the zincs should be in the heat exchange at the raw water chamber. Unless the heat exchange is made of bronze that no need zinc.
 

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I took the 2 plugs out that are supposed to have zincs on my raw water cooled 2QM15 yesterday. Only thing left is the threaded piece that screws into the cap that the zinc is supposed to be attaced to. Perhaps I should have not given up so easy last time I tried to get to the front zinc. This time a 2' cheater pipe on the end of wrench was just enough leverage to get it out.:eek: I hope your goes better!!!!!!!
 

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This has been debated many times over the years. My last two boats have had Yanmar 3GM30F engines. I attended the Mack Boring diesel engine course. This engine does not have a zinc in the cooling system. Here is some of the text from my engine course.

"Yanmar uses cupronickel heat exchangers. Extremely low to non existant corrosion factor so no zincs fitted. Most engine mfg use copper heat exchangers which need a zinc to keep corrosion at bay."

I cannot speak for the QM series as I have no experience, but if it is a GM-F series don't worry about it. To my knowledge the only small Yanmars with zincs are the directly raw water cooled models.
 

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Discussion Starter · #11 ·
Thanks for the info!

Hey guys,

Thanks for all your responses. Its a great credit to sailnet that my question was answered in less than 4 hours. :)

A call to my local dealer confirmed that my 3GM30F did in fact have a cupronickel heat exchanger (as do all the fresh-water cooled GM series) that needed no zinc.

I sure wish they had thought to write that in the manual!!

...now, if someone can only invent a prop and shaft that doesn't need a zinc, that will be one less thing to think about every year...

Regards,

--
Joe
 

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Wew...had me goin there

I was ready to contact my mechanic...glad they're not 'there' Yay, sailnet! :)
 

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Since this questions was answered I figured it wouldn't be too much of a problem to slightly high-jack the thread...

I have the 3GMD which I believe is the raw water cooled version of the engine everyone was discussing. I know for sure it has 2 zincs. The engine was completely ripped apart and re-built, having many of the parts re-machined in 2005 by the previous owner who was a mechanic. It runs absolutely perfect. My question is, since it is raw-water cooled and take into consideration it was rebuilt in 05' what is the life expectancy before I start seeing problems from corrosion from the salt water?

I have asked many people about doing the fresh water conversion and they basically said that they have seen bad results doing it on a 1983 engine that has been raw water cooled it's whole life. Basically if it ain't broke - why fix it.

Would like to hear some opinions - thanks
 

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I would think the zinc's would be replaced at least every year or sooner
 

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I have asked many people about doing the fresh water conversion and they basically said that they have seen bad results doing it on a 1983 engine that has been raw water cooled it's whole life. Basically if it ain't broke - why fix it.

Would like to hear some opinions - thanks
Leave it as is. It will be fine for years and years and years. Save your pennies in the meanwhile. When it finally conks at the end of next decade, buy a new, fwc engine.
 

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When I replaced the front zinc in my Yanmar 2QM15 raw water cooling, the housing turned as well and pinched the hose. I did not know this at that time until I went out cruising and found water under the engine. I had to remove the alternator and use vice grip to hold the housing so it will not turn when I remove the plug. I cut off about half inch of the hose where the damage was and put it back in. Yes it was pain in the neck to replace the front zinc. I use my boat in salt water area so zinc replacement is a must do thing. I suppose if you use the boat on the fresh water area such as lake Ontario you may not to worry about zinc even the engine is raw water cooling.
 

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Zinc pencil on yanmar 3gm30f

I saw this post from a couple of years ago and am wondering how it turned out. I have the same engine and the manual I have (from yanmar) shows at least 2 zincs. I have been trying to find them but maybe I can relax?
 

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We have the 3GM30F no zincs on ours
 
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