I just had to clean out some black crud from my exhaust elbow on my Yanmar 2GM20 which was the cause of some overheating. Now, I've just learned from a very good source that the reason an exhaust elbow will plug up is because of iron oxadization caused by the raw water coolant system zincs needing replacment (salt water attacking the cooling jacket!!). Problem is I don't have a clue where the zincs are or how to replace them. Do any of you 2GM20 owners know where the zincs reside and how to replace them??
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Terry Arnold
zinc locations
I don't see how there is any connection between exhaust elbow carbon and zincs, but that doesn't change the importance of the zincs, which is to prevent or minimize corrosion of the water passages in the engine. There are two zincs, one at side cover of cylinder head, (rear) and one on cylinder block on exhaust side, above fuel pump. They are accessed by removing the large hex nut plugs which may still have a sticker on its face identifying the plug as the zinc. Yanmar manual recommends replacing the zincs after 500 hours or after 50 % corrosion loss.
I don't see how there is any connection between exhaust elbow carbon and zincs, but that doesn't change the importance of the zincs, which is to prevent or minimize corrosion of the water passages in the engine. There are two zincs, one at side cover of cylinder head, (rear) and one on cylinder block on exhaust side, above fuel pump. They are accessed by removing the large hex nut plugs which may still have a sticker on its face identifying the plug as the zinc. Yanmar manual recommends replacing the zincs after 500 hours or after 50 % corrosion loss.
Not sure that is true!
Bert: The mixing elbows on Yanmar all coke up evenutally in salt water. This is just a maintenance item. I think that there is a recommendation that these be replaced every 3-6 years. If you run you engine at the recommended RPM's (70-80% of max rated RPM's) you can extend this time. MY understanding is that this is caused because of the chemical reaction in the exhaust, heat and the salt water. Obviously you need to do the zinc inspection regardless if this is the cause or not.
Bert: The mixing elbows on Yanmar all coke up evenutally in salt water. This is just a maintenance item. I think that there is a recommendation that these be replaced every 3-6 years. If you run you engine at the recommended RPM's (70-80% of max rated RPM's) you can extend this time. MY understanding is that this is caused because of the chemical reaction in the exhaust, heat and the salt water. Obviously you need to do the zinc inspection regardless if this is the cause or not.
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Roy Mosteller
2GM20F Has No Zincs
Acknowledging that the 2GM20 Manual speaks of replacing zincs in the cooling water system I talked this morning with my YANMAR dealer mechanic. He assures me that zincs in a 2GM20 apply only to raw water cooled engines. If the model is 2GM20F (closed fresh water cooled) there are no zincs on the engine. Hope this helps as we occasionally see this question discussed here.
Acknowledging that the 2GM20 Manual speaks of replacing zincs in the cooling water system I talked this morning with my YANMAR dealer mechanic. He assures me that zincs in a 2GM20 apply only to raw water cooled engines. If the model is 2GM20F (closed fresh water cooled) there are no zincs on the engine. Hope this helps as we occasionally see this question discussed here.
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Bert Kinyon
This is a raw water system
Yes, this is a raw water system with a heat exchanger to an internal sealed system. Does anyone have a photograph showing where these zincs are located?
Yes, this is a raw water system with a heat exchanger to an internal sealed system. Does anyone have a photograph showing where these zincs are located?
Bert, read his lips!
Bert: As Ron stated. There are NO zincs on a 2GM20F. You originally stated that you have a 2GM20 (not an F) The real cause of coking! Running your engine below 2500RPM's for extended periods of time. This will NOT prevent it the coking. Moving your boat to salt water would help with the corrosion.
Bert: As Ron stated. There are NO zincs on a 2GM20F. You originally stated that you have a 2GM20 (not an F) The real cause of coking! Running your engine below 2500RPM's for extended periods of time. This will NOT prevent it the coking. Moving your boat to salt water would help with the corrosion.
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Bert Kinon
Never been out of saltwater...
Steve, This boat has never seen fresh water. It has been in San Francisco bay ever since I bought it new.
Steve, This boat has never seen fresh water. It has been in San Francisco bay ever since I bought it new.
Slip of the finger!
Bert: What I meant to say was moving it to 'fresh water'. I really do not think that you can prevent the corrosion. Hot exhaust, acids from the fuel and salt water all mix together in the elbow and become very corrosive. The elbow is just a maintenance item that needs to inspected every year or two and replaced as necessary. Sorry for the mis-que. I knew what I meant, how come you didn't<haha>.
Bert: What I meant to say was moving it to 'fresh water'. I really do not think that you can prevent the corrosion. Hot exhaust, acids from the fuel and salt water all mix together in the elbow and become very corrosive. The elbow is just a maintenance item that needs to inspected every year or two and replaced as necessary. Sorry for the mis-que. I knew what I meant, how come you didn't<haha>.
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Bert Kinon
The "mechanics" of electrolasis
I've been told that zincs on the bottom of the boat will do little to protect internal engine parts exposed to pumped sea water. The reason being that the water being pumped through the engine is traveling at a much faster rate then the boat through water. Not being an expert I'm curious to learn if others have heard this as well. Since zinc's work on an electrical basis I would think the speed of the water would be of little or no consequence when compared to the speed of electricity.... Just gotta keep turning over those stones..... ;-)
I've been told that zincs on the bottom of the boat will do little to protect internal engine parts exposed to pumped sea water. The reason being that the water being pumped through the engine is traveling at a much faster rate then the boat through water. Not being an expert I'm curious to learn if others have heard this as well. Since zinc's work on an electrical basis I would think the speed of the water would be of little or no consequence when compared to the speed of electricity.... Just gotta keep turning over those stones..... ;-)
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