For many years my 1GM10 has had problems during the hotter months (July/August). When in gear and at or near idle, it boggs down and rpm falls to around 500. It runs quite rough at that speed. It produces a little sooty exhaust when running rough (high vibration, low rpm, varying rpm)and has no noticeable ehxhaust at any other time. At the high end, it seems to run a little slower (around 2800) than normal (around 3000). When it is in neutral, the problem seldom occurs and the idle speed remains at specs. The rest of the year there is no problem with the engine. I have checked each year for water in the fuel, bacteria, air in the lines, replaced fuel filters (primary and secondary), cleaned the vent, checked the injectors, changed the oil, replaced air filters, etc. I have never located the problem, but it has been persistent. I have used 20, 30 and 40 wt oil at various times. The fuel supply seems clear of obstructions and it is easy to pump by hand or siphon through the fuel line. I have not drained the tank and filtered the fuel since it seems quite clean from the fuel line and the filters are consistently clean and new looking on removal. As best I can tell, the timing is OK since there is no problem for most of the year. I have not checked the fuel tank itself, but would not expect any internal problems that it could have to be so consistently tied to the weather. I have tried cetane boosters, bug killers, water treatments, and other things as well. The engine tends to get regular workouts (not just for getting out of the marina). Any ideas would be appreciated. The engine is cared for rather well, but by a person who has little mechanical knowledge (me).
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500 RPM's too low!
John: The specs for this engine are a min of 850+/- 25 RPMs at idle and max of 3825 +/- 50 at no load. I think your engine must shake, rattle and roll at this low RPM setting. Try idling up to 800-900 RPM and see if that does not help the low end problem. I would stay away from any oil other than 30 wt or 15-40 per Yanmar Specs. You need to be sure that your bottom and prop are not fouled (just went thru this in the last week or so with another boat on this site). You also need to see if you have the propper prop for you boat. Just because it is factory spec, does not mean that it is correct. If the boat has too large of a prop you will not be able to get the performance out of it. You should be able to rev somewhere at the 3400-3600 RPM when in gear. Your operating range is in the 2500-3000 RPM range.
John: The specs for this engine are a min of 850+/- 25 RPMs at idle and max of 3825 +/- 50 at no load. I think your engine must shake, rattle and roll at this low RPM setting. Try idling up to 800-900 RPM and see if that does not help the low end problem. I would stay away from any oil other than 30 wt or 15-40 per Yanmar Specs. You need to be sure that your bottom and prop are not fouled (just went thru this in the last week or so with another boat on this site). You also need to see if you have the propper prop for you boat. Just because it is factory spec, does not mean that it is correct. If the boat has too large of a prop you will not be able to get the performance out of it. You should be able to rev somewhere at the 3400-3600 RPM when in gear. Your operating range is in the 2500-3000 RPM range.
R
red coles
critters
Just a thought, but since it only happens in warm water months, perhaps you have some growth or fouling on prop or shaft. Good luck red
Just a thought, but since it only happens in warm water months, perhaps you have some growth or fouling on prop or shaft. Good luck red
J
Jay Kent
I finally have an answer for my issues
on the same engine in a H27. I had a 13 x 10, 1 inch prop delivered to me this past week. When the boat was pulled, we found that the previous marina had replaced a damaged prop (13 x 10, which I still have) with a 13 x 11. This difference in pitch resulted in heavy black smoke being emitted from the exhaust and fouling the stern, badly. We kept cleaning and cleaning, while we had every possible problem checked out, one at a time...process of elimination. All the experts predicted that it was the wrong size or pitch of a prop. Well, we were getting 3100 at no load and 2800 at full load. When we put the boat back in, there was this huge puff of black smoke that created a cloud in the cockpit and then it cleared. We now have 3800 no load and 3400 at full load and NO BLACK SMOKE!! The black smoke is a sign of unburnt diesel fuel and shows that the engine is "loading up". We had lots of opportunity to run her this past weekend, as the wind died and we motored back from a relaxing "anchorage" on Sunday for 3 1/2 hours. No smoke, and running great!! So, the price of a new prop, lift out and change out of prop (prop puller rental)has gotten us the solution we had been seeking. Hope your's gets resolved, too, and that this information may be of help.
on the same engine in a H27. I had a 13 x 10, 1 inch prop delivered to me this past week. When the boat was pulled, we found that the previous marina had replaced a damaged prop (13 x 10, which I still have) with a 13 x 11. This difference in pitch resulted in heavy black smoke being emitted from the exhaust and fouling the stern, badly. We kept cleaning and cleaning, while we had every possible problem checked out, one at a time...process of elimination. All the experts predicted that it was the wrong size or pitch of a prop. Well, we were getting 3100 at no load and 2800 at full load. When we put the boat back in, there was this huge puff of black smoke that created a cloud in the cockpit and then it cleared. We now have 3800 no load and 3400 at full load and NO BLACK SMOKE!! The black smoke is a sign of unburnt diesel fuel and shows that the engine is "loading up". We had lots of opportunity to run her this past weekend, as the wind died and we motored back from a relaxing "anchorage" on Sunday for 3 1/2 hours. No smoke, and running great!! So, the price of a new prop, lift out and change out of prop (prop puller rental)has gotten us the solution we had been seeking. Hope your's gets resolved, too, and that this information may be of help.
B
Bill O'Donovan
Mixing elbow
Typically your symptoms suggest that the mixing elbow is coked up with exhaust and rust. They are not worth fixing but should be replaced instead. There's plenty on this in the Archives, and many marina stores carry the elbows because the problem is so pervasive. An easier alternative is to check the L-shaped hose that takes the raw water to the strainer. Sometimes they're jury-rigged to bend the hose, when instead they have to be pre-formed in an L. Any auto repair store has them in stock, and it's a lot easier to replace that than the mixing elbow.
Typically your symptoms suggest that the mixing elbow is coked up with exhaust and rust. They are not worth fixing but should be replaced instead. There's plenty on this in the Archives, and many marina stores carry the elbows because the problem is so pervasive. An easier alternative is to check the L-shaped hose that takes the raw water to the strainer. Sometimes they're jury-rigged to bend the hose, when instead they have to be pre-formed in an L. Any auto repair store has them in stock, and it's a lot easier to replace that than the mixing elbow.
K
Ken Cobb
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