My recent trip to Block Island was plagued by the Yanmar 3GM30F (2003 H356) slowing in rpms at odd times. I was running at 3,000 rpm but the engine would slow to about 2,000 rpm for perhaps 15 seconds (causing an immediate concern that it was going to quit) and without any intervention it would recover and return to 3,000 rpm. This would happen at intervals ranging from 15 minutes to an hour but it became so regular that the crew came to ignore it. I wonder if it could be fuel filters (changed at launch this spring)or something causing fuel starvation. The irregularity may point to something in the tank that moves in front of the intake. We did a 10 hour run (wing and wing) down Long Island Sound with lots of following waves and then had a great deal of difficulty starting the engine at the end of the trip. Could be unrelated but I am unsure. Any similar experience and solution will be appreciated.
Yanmar rpm slows and recovers.
- Thread starter Tom C5878
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yanmar slowing and recovering
Tom, this sounds like biocrud in your tank-it normally settles to the bottom, but running in a sea can stir it up enough to get sucked into the pickup-and it can form large enough chunks to clog a pickup temporarily. since you've got new filters, if you have old fuel in the tank you may want to get it polished
Tom, this sounds like biocrud in your tank-it normally settles to the bottom, but running in a sea can stir it up enough to get sucked into the pickup-and it can form large enough chunks to clog a pickup temporarily. since you've got new filters, if you have old fuel in the tank you may want to get it polished
Diesel Bug
Tom, These are classic symptoms of diesel bug. Look into your tank and remove the fine mesh strainer on the end of the pickup tube. If you find loads of muck in the tank then it will need to be pumped out and the tank cleaned. I've been there - twice - and it is not pleasant; so I add "Fuel Set" to every tankful of fuel. And its dangerous too. It takes about three days after you buy the diesel with water for this condition to manifest itself. I do not support the theory that it is condensation inside your tank as, on both occasions it took exactly 3 days after I bought fuel from marinas where the tank sits in the water and, on both occasions, the marina's tank had just been refilled. A pal who is a Shell Executive told me that they are supposed to allow 4 hours for the muck to settle before selling any fuel, and they are supposed to clean their tanks every three months. He also said that a good marina will do it about every two years and a bad one never.
Tom, These are classic symptoms of diesel bug. Look into your tank and remove the fine mesh strainer on the end of the pickup tube. If you find loads of muck in the tank then it will need to be pumped out and the tank cleaned. I've been there - twice - and it is not pleasant; so I add "Fuel Set" to every tankful of fuel. And its dangerous too. It takes about three days after you buy the diesel with water for this condition to manifest itself. I do not support the theory that it is condensation inside your tank as, on both occasions it took exactly 3 days after I bought fuel from marinas where the tank sits in the water and, on both occasions, the marina's tank had just been refilled. A pal who is a Shell Executive told me that they are supposed to allow 4 hours for the muck to settle before selling any fuel, and they are supposed to clean their tanks every three months. He also said that a good marina will do it about every two years and a bad one never.
I support the idea...
...of the following posts. Diesels usually slow down or quit because of fuel problems. And since you have changed your filters this season, it narrows it down to, most likely, fuel problems.
...of the following posts. Diesels usually slow down or quit because of fuel problems. And since you have changed your filters this season, it narrows it down to, most likely, fuel problems.
Plugged exhaust riser
My Yanmar 3HM35 did the same thing and finally quit running. It would still start and then die in a few seconds. We spent a week troubleshooting it, got the injectors and pump tested after all of the usual things. We checked everything, used a second fuel source and it still did not work. It turned out that the riser was completely blocked by carbon and rust. The initial symptoms were exactly as you have described with the rpm dropping for a while and then coming back up. The exhaust riser is the upside down "u" shaped part at the end of the exhaust manifold where the cooling water is injected into the exhaust gas to cool it before it passes into the rubber exhaust hose. To check it out, just pull off the hose at the end and see if it is full of crud by sticking a screwdriver up inside. Four bolts hold it onto the exhaust manifold on mine so it is easy to remove and replace. If it isn't broken, just clean it out and put it back on. Mine is finally cracked and needs replacement. See my other post. Price for a new one varies widely - $55 to as much as $480.
My Yanmar 3HM35 did the same thing and finally quit running. It would still start and then die in a few seconds. We spent a week troubleshooting it, got the injectors and pump tested after all of the usual things. We checked everything, used a second fuel source and it still did not work. It turned out that the riser was completely blocked by carbon and rust. The initial symptoms were exactly as you have described with the rpm dropping for a while and then coming back up. The exhaust riser is the upside down "u" shaped part at the end of the exhaust manifold where the cooling water is injected into the exhaust gas to cool it before it passes into the rubber exhaust hose. To check it out, just pull off the hose at the end and see if it is full of crud by sticking a screwdriver up inside. Four bolts hold it onto the exhaust manifold on mine so it is easy to remove and replace. If it isn't broken, just clean it out and put it back on. Mine is finally cracked and needs replacement. See my other post. Price for a new one varies widely - $55 to as much as $480.
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