I'll try to make a long story short... When we purchased Destiny last year we had starting problems, and I had to bleed the engine (Yanmar 4JH-TE) whenever she sat for more than 3-4 days. I searched in vain for air leaks around the fuel system. Earlier this year I had the yard look into it, and they found that there was a leak in the small (about 1/8" diam.) rubber cap on the end of the fuel return line, at the last injector in the chain. Made sense, that would let air into the system. They didn't have the Yanmar part so they put a temporary cap on, with the promise to install the proper part as soon as it came in. Everything worked great, the engine would start immediately, until about a month ago, when the same starting problems started again. The yard said that they had put the Yanmar cap on. Yesterday I decided it was time to get to the bottom of the problem again. The engine would not start, despite bleeding it twice. When I went down to the engine room after cranking, I could hear a whistling sound, like air being sucked in somewhere around the injectors. As soon as I touched the new rubber cap on the return line it broke and fell right off! It was as if it was rotten, and it crumbled between my fingers. That was obviously the problem. So my question is: what destroyed that rubber cap in less than four months? Are there some rubber-like materials that are "eaten" by diesel? And the bigger question for me is - did the yard in fact use the proper Yanmar part? I'll be on their doorstep at 8am tomorrrow!) Derek
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Jose Venegas
Diesel eats plastic
Derek, my Beneteau 361 has the stern shower control just below the diesel tank vent. As a result, in more than one occasion a small amount of diesel spilled out and wetted the plastic lid covering the shower control valve. This season I noted that the strip of material holding the lid cover had a crack and was ready to fall off. The lid material was crystallized and had become weak and brittle. I could cut it with my nail. I don't know if rubber has the same response to diesel as this plastic, but it is possible that what they replaced in your engine was made of the same type of plastic as my lid.
Derek, my Beneteau 361 has the stern shower control just below the diesel tank vent. As a result, in more than one occasion a small amount of diesel spilled out and wetted the plastic lid covering the shower control valve. This season I noted that the strip of material holding the lid cover had a crack and was ready to fall off. The lid material was crystallized and had become weak and brittle. I could cut it with my nail. I don't know if rubber has the same response to diesel as this plastic, but it is possible that what they replaced in your engine was made of the same type of plastic as my lid.
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steven f.
hydrocarbons
I'm NOT a chemist by any means but it seems to me that since diesel fuel and many generic rubber products are both made from hydrocarbons that the fuel could vary well slowly disolve the rubber. I realize some parts are rubber-like but I'm guessing that they are specifically designed to be used in/around fuel products. Now hopefully you will hear from someone who actually knows what he is talking about instead of me....
I'm NOT a chemist by any means but it seems to me that since diesel fuel and many generic rubber products are both made from hydrocarbons that the fuel could vary well slowly disolve the rubber. I realize some parts are rubber-like but I'm guessing that they are specifically designed to be used in/around fuel products. Now hopefully you will hear from someone who actually knows what he is talking about instead of me....
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Rob
OK, I'm a chemist.
Diesel damages natural rubber. There are rubber-like materials that are not severly damaged by diesel. See the link below for a quick chemical compatibility search (lists results for many materials). Try "Diesel Fuel" for the chemical and submit. Rubber-like materials that are listed as not severely damaged include Buna-N (nitrile), Hapalon, Viton and neoprene. Take note of the disclaimers at the bottom of the results page. I do not think they were tested under the operating conditions of an engine. Maybe we should try a diesel systems engineer.
Diesel damages natural rubber. There are rubber-like materials that are not severly damaged by diesel. See the link below for a quick chemical compatibility search (lists results for many materials). Try "Diesel Fuel" for the chemical and submit. Rubber-like materials that are listed as not severely damaged include Buna-N (nitrile), Hapalon, Viton and neoprene. Take note of the disclaimers at the bottom of the results page. I do not think they were tested under the operating conditions of an engine. Maybe we should try a diesel systems engineer.
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Jose Venegas
Silicone Rubber is badly affected..
.. by diesel according to Rob's great link. It predicts severe effect of Diesel on Silicone. NOT RECOMMENDED FOR ANY USE !!! That may explain the effect of diesel on my shower valve lid. May be the replaced part on Dereck's engine was also made of silicone rubber.
.. by diesel according to Rob's great link. It predicts severe effect of Diesel on Silicone. NOT RECOMMENDED FOR ANY USE !!! That may explain the effect of diesel on my shower valve lid. May be the replaced part on Dereck's engine was also made of silicone rubber.
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Larry W.
rubbers
I'm no chemist, either, but I don't think rubber is a hydrocarbon. Isn't real rubber a processed tree sap? Does the processing use hydrocarbons? If diesel fuel attacks rubber, why is rubber, the more natural the better, used in fuel hoses?
I'm no chemist, either, but I don't think rubber is a hydrocarbon. Isn't real rubber a processed tree sap? Does the processing use hydrocarbons? If diesel fuel attacks rubber, why is rubber, the more natural the better, used in fuel hoses?
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Rob
More on rubber
Larry, lotsa questions. I see that you have interest in this thread like I do. Let me start this with saying that I do not daily work with the applications of various elastomeric compounds. I am not an expert on the subject of rubber. I hope that by using my background I can find and provide more technically-based information. I bet the people over at Goodyear Tire and Rubber would be great on this one. That said, back to the original question of "Are there some rubber-like materials that are "eaten" by diesel?" The answer is again yes, there are some. Other answers: Yes, real rubber (natural rubber) comes from the sap. It is also chemically known as cis-1,4-polyisoprene. It contains only the elements of hydrogen and carbon. It is a hydrocarbon. The oil we fry our chicken in is also a hydrocarbon produced by plants like corn and soybeans. "Does the processing use hydrocarbons?" Good question. I do not know. "...why is rubber, the more natural the better, used in fuel hoses?" I am under the impression that manufacturers commonly use NBR rubber (a copolymer of 1,3-butadiene and acrylonitrile) for fuel lines due to its high resistance to being damaged by fuel and oil. It is not the same material as natural rubber. Lastly. I am all rubbered out. Time to go sailing.
Larry, lotsa questions. I see that you have interest in this thread like I do. Let me start this with saying that I do not daily work with the applications of various elastomeric compounds. I am not an expert on the subject of rubber. I hope that by using my background I can find and provide more technically-based information. I bet the people over at Goodyear Tire and Rubber would be great on this one. That said, back to the original question of "Are there some rubber-like materials that are "eaten" by diesel?" The answer is again yes, there are some. Other answers: Yes, real rubber (natural rubber) comes from the sap. It is also chemically known as cis-1,4-polyisoprene. It contains only the elements of hydrogen and carbon. It is a hydrocarbon. The oil we fry our chicken in is also a hydrocarbon produced by plants like corn and soybeans. "Does the processing use hydrocarbons?" Good question. I do not know. "...why is rubber, the more natural the better, used in fuel hoses?" I am under the impression that manufacturers commonly use NBR rubber (a copolymer of 1,3-butadiene and acrylonitrile) for fuel lines due to its high resistance to being damaged by fuel and oil. It is not the same material as natural rubber. Lastly. I am all rubbered out. Time to go sailing.
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