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16-11-2020, 16:37
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#1
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Senior Cruiser
Join Date: Nov 2017
Location: USA, NH
Boat: Pearson 33-2 1988
Posts: 272
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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
__________________
diane
s/v Desiderata
"The cure for anything is saltwater - sweat, tears or the sea." Isak Dinesen
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16-11-2020, 18:36
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#2
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Marine Service Provider
Join Date: Sep 2014
Location: Auckland, NZ
Boat: Compass 790 , 7.9 metres or 26 ft
Posts: 2,803
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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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16-11-2020, 19:47
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#3
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Registered User
Join Date: Apr 2005
Location: Southern California
Boat: Catalina 320
Posts: 1,308
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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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16-11-2020, 22:13
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#4
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,305
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Re: Sacrificial Anodes?
Is your engine a 2GM20 or a 2GM20F?
The 2GM20 requires anodes and the 2GM20F does not.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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17-11-2020, 03:36
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#5
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,305
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Re: Sacrificial Anodes?
Quote:
Originally Posted by djousset
............
I have a Yanmar 2GM20 and although the diesel guide references them I can't seem to locate them.........
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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.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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17-11-2020, 04:17
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#6
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Senior Cruiser
Join Date: Nov 2017
Location: USA, NH
Boat: Pearson 33-2 1988
Posts: 272
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Re: Sacrificial Anodes?
Quote:
Originally Posted by Wotname
Is your engine a 2GM20 or a 2GM20F?
The 2GM20 requires anodes and the 2GM20F does not.
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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.
__________________
diane
s/v Desiderata
"The cure for anything is saltwater - sweat, tears or the sea." Isak Dinesen
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17-11-2020, 04:53
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#7
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Registered User
Join Date: Sep 2009
Location: Houston
Boat: ‘01 Catana 401
Posts: 9,626
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Re: Sacrificial Anodes?
Quote:
Originally Posted by djousset
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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Do you also have a radiator cap and an exhaust manifold filled with a colored coolant?
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17-11-2020, 04:55
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#8
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,305
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Re: Sacrificial Anodes?
Quote:
Originally Posted by djousset
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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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.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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17-11-2020, 06:11
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#9
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Senior Cruiser
Join Date: Nov 2017
Location: USA, NH
Boat: Pearson 33-2 1988
Posts: 272
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Re: Sacrificial Anodes?
Quote:
Originally Posted by Wotname
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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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?
__________________
diane
s/v Desiderata
"The cure for anything is saltwater - sweat, tears or the sea." Isak Dinesen
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17-11-2020, 13:27
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#10
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Senior Cruiser
Join Date: Nov 2017
Location: USA, NH
Boat: Pearson 33-2 1988
Posts: 272
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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!
__________________
diane
s/v Desiderata
"The cure for anything is saltwater - sweat, tears or the sea." Isak Dinesen
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17-11-2020, 14:35
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#11
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,305
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Re: Sacrificial Anodes?
Quote:
Originally Posted by djousset
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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Quote:
Originally Posted by djousset
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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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.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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17-11-2020, 16:37
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#12
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Senior Cruiser
Join Date: Nov 2017
Location: USA, NH
Boat: Pearson 33-2 1988
Posts: 272
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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.
__________________
diane
s/v Desiderata
"The cure for anything is saltwater - sweat, tears or the sea." Isak Dinesen
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17-11-2020, 16:48
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#13
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,305
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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
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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17-11-2020, 16:54
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#14
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Senior Cruiser
Join Date: Nov 2017
Location: USA, NH
Boat: Pearson 33-2 1988
Posts: 272
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Re: Sacrificial Anodes?
Will do, Thanks again.
__________________
diane
s/v Desiderata
"The cure for anything is saltwater - sweat, tears or the sea." Isak Dinesen
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18-11-2020, 05:15
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#15
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Registered User
Join Date: Oct 2015
Location: Wisconsin
Boat: 1999 Jeanneau 36.2
Posts: 61
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Re: Sacrificial Anodes?
Quote:
Originally Posted by Calif.Ted
Freshwater cooled GM series engines do not have a pencil zinc, raw water cooled engines do.
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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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