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Old 16-11-2020, 17:37   #1
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Sacrificial Anodes?

I've been consistent on replacing the zincs my the shaft but recently became aware of sacrificial engine anodes in a thread I was following and realize I should be paying attention to that. I have a Yanmar 2GM20 and although the diesel guide references them I can't seem to locate them. One article spoke of them as if they were optional....? I am on to other things but have added this to my spring list. Any guidance would be appreciated, the simpler the terms the better (newbie) as relates to the engine.
Thanks! D
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Old 16-11-2020, 19:36   #2
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Re: Sacrificial Anodes?

They aint optional particularly in salt water!
If you dont replace them as needed the block will rust out

There is a service manual for your engine in the CF library which will tell you about them but Wotname may help you as he's had those engines & he's good at writing instructions for novices.


Does your engine have a heat exchanger? as there are 2 versions of the 2GM20.
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Old 16-11-2020, 20:47   #3
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Re: Sacrificial Anodes?

Freshwater cooled GM series engines do not have a pencil zinc, raw water cooled engines do.
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Old 16-11-2020, 23:13   #4
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Re: Sacrificial Anodes?

Is your engine a 2GM20 or a 2GM20F?

The 2GM20 requires anodes and the 2GM20F does not.
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Old 17-11-2020, 04:36   #5
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Re: Sacrificial Anodes?

Quote:
Originally Posted by djousset View Post
............
I have a Yanmar 2GM20 and although the diesel guide references them I can't seem to locate them.........
There are two, one is located on the block (exhaust side) near the block drain plug and the fuel lift pump. The other is located on the aft end of the head.

If they haven't been removed for some time, they can be very very tight. I suggest a decent size breaker bar. You will need a 24mm socket or ring wrench.
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Old 17-11-2020, 05:17   #6
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Re: Sacrificial Anodes?

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Originally Posted by Wotname View Post
Is your engine a 2GM20 or a 2GM20F?

The 2GM20 requires anodes and the 2GM20F does not.
The manual the prior owner provided notes 2GM20F. I have been confused because I thought the "F" meant fresh water, however I have a raw (salt) water intake.
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Old 17-11-2020, 05:53   #7
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Re: Sacrificial Anodes?

Quote:
Originally Posted by djousset View Post
The manual the prior owner provided notes 2GM20F. I have been confused because I thought the "F" meant fresh water, however I have a raw (salt) water intake.


Do you also have a radiator cap and an exhaust manifold filled with a colored coolant?
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Old 17-11-2020, 05:55   #8
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Re: Sacrificial Anodes?

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Originally Posted by djousset View Post
The manual the prior owner provided notes 2GM20F. I have been confused because I thought the "F" meant fresh water, however I have a raw (salt) water intake.
OK.

This might help - the 'F' means the engine is cooled by fresh water or more commonly, by 'coolant'. The coolant circulates through the engine and also through the heat exchanger (usually bolted onto the engine and often part of the exhaust manifold).

The heat exchanger is then cooled by raw salt water. That is why you have a raw salt water intake. This salt water never enters the engine. It goes from the intake, through the raw water pump, then into the heat exchanger and finally into the exhaust.
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Old 17-11-2020, 07:11   #9
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Re: Sacrificial Anodes?

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OK.

This might help - the 'F' means the engine is cooled by fresh water or more commonly, by 'coolant'. The coolant circulates through the engine and also through the heat exchanger (usually bolted onto the engine and often part of the exhaust manifold).

The heat exchanger is then cooled by raw salt water. That is why you have a raw salt water intake. This salt water never enters the engine. It goes from the intake, through the raw water pump, then into the heat exchanger and finally into the exhaust.
Thank you Wotname, this does help. I do have a place to add coolant, and a "reservoir" or overflow. So back to the beginning, does this mean I do have anodes to check?
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Old 17-11-2020, 14:27   #10
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Re: Sacrificial Anodes?

Curiosity (aka worry) sent be aboard today and yes, I do have zinc anodes. I'm so happy I asked and thank you for the guidance!
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Old 17-11-2020, 15:35   #11
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Re: Sacrificial Anodes?

Quote:
Originally Posted by djousset View Post
Thank you Wotname, this does help. I do have a place to add coolant, and a "reservoir" or overflow. So back to the beginning, does this mean I do have anodes to check?
Quote:
Originally Posted by djousset View Post
Curiosity (aka worry) sent be aboard today and yes, I do have zinc anodes. I'm so happy I asked and thank you for the guidance!
Being as you have confirmed your engine is coolant cooled, you don't need to check the anodes (even if they are fitted).

The anodes will no longer be functional and replacing them is a waste of time and effort.

If the engine came from Yanmar as a 2GM20F (ie as stated on the name plate) then the external plugs you can see will not have anodes attached to them inside the engine.

If the engine was originally a 2GM20 and a previous owner converted it to a 2GM20F, the anodes may have been left in place during the conversion; however they will serve no purpose.
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Old 17-11-2020, 17:37   #12
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Re: Sacrificial Anodes?

Wotname I'll admit I am a bit confused, as the prior owner has the "anticorrosion zinc" underlined, circled and starred in the manual, he also has the model # 2GM20F underlined, circled and starred. (Perhaps he was confused as well...) I will check the nameplate but I am hearing that as long as there is coolant for the engine, and the raw water intake is for the heat exchanger then I can cross zinc anodes off my list.
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Old 17-11-2020, 17:48   #13
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Re: Sacrificial Anodes?

I guess I can't speak for every 2GM20F ever made by Yanmar over the years, perhaps some did have factory fitted anodes at some point in time.

I haven't seen one with yet but you never know. The manual I use do not mention them.

If you do find anodes fitted on the anode plugs and the name plate is states 2GM20F, do let us know via this thread.

Assuming they are zinc, rest assured they will be ineffectual when using either coolant or fresh water in the engine cooling system. AFAIK, Yanmar has never made a magnesium anode for this engine although someone else may have made a DIY magnesium anode.

Have a look at this thread - https://www.cruisersforum.com/forums...ng-242526.html

and this https://www.fisheriessupply.com/unde...ificial-anodes
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Old 17-11-2020, 17:54   #14
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Re: Sacrificial Anodes?

Will do, Thanks again.
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Old 18-11-2020, 06:15   #15
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Re: Sacrificial Anodes?

Quote:
Originally Posted by Calif.Ted View Post
Freshwater cooled GM series engines do not have a pencil zinc, raw water cooled engines do.

My 3GM30F (freshwater) does have a zinc. Located on the starboard side of the engine block, tucked just below the heat exchanger, slighly aft. It's a large hex plug screwed into the block. The zinc is screwed into the inside of that plug.
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