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Old 30-03-2009, 08:35   #1
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RPM's Yanmar 3GM engine

The po said that he never exceeded 2000 RPM and cruised at about 1800. We are reading that some of you are running at 3000 RPM. We are confused as to this discrepancy. What is recommended practice?
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Old 30-03-2009, 09:24   #2
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The yanmar mechanics I talked to recommended you run it at near max rpm. Then again, they get to replace the cracked pistons!
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Old 30-03-2009, 10:45   #3
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The po said that he never exceeded 2000 RPM and cruised at about 1800. We are reading that some of you are running at 3000 RPM. We are confused as to this discrepancy. What is recommended practice?
The owners manual says to not run the engine for extended periods at less than 80% throttle to prevent glazing of the cylinder walls and other problems which I forget at the moment. It goes on to say that if you are going to run for extended times at low loads that you should run the engine up to at least 80% throttle, IIRC for about 5 minutes every couple of hours. 80% of max rpm is around 2900 rpm.

There are many threads about diesel engine load on this forum. Basically there is a group of people out in the world that believes running your diesel at light loads is good for it, the mechanics here will tell you otherwise.

John
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Old 30-03-2009, 12:25   #4
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Would the engine be loaded heavier at lower rpm or higher rpm? Seems to me turning the same size prop at either rpm, pushing the same load, lower rpm would load the engine more..... Running at near max rpm, both my Yanmar 28 hp went bad prior to 3000 hours.... cracked pistons....
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Old 30-03-2009, 12:47   #5
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The manual for the 3GM30 sais that max continous RPM is 3400 or 3600 for no more than an hour. Diesels should, as previously stated, always be run under heavy load.
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Old 31-03-2009, 07:55   #6
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As far as I know, there’s two principle reasons to run a diesel hard (about 80% of Continuous RPM):
1. Diesels must run at design temperatures (± 190 F / 88 C), which generally requires higher RPMs.
2. Engines achieve their highest efficiency (HP : Fuel Burn) at about these RPMs.

It should be noted that Yanmar Tachometers often read a little lower (-100 RPM) than actual RPM.
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Old 31-03-2009, 08:03   #7
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My understanding about the importance of running a diesel under load is to keep the oil temperature up to operating level. At least that is what my guru Steve D'Antonio tells me . The coolant temperature will come up to operating level under very light load (on most engines) but the oil temperature will not.
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Old 31-03-2009, 08:21   #8
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Would the engine be loaded heavier at lower rpm or higher rpm? Seems to me turning the same size prop at either rpm, pushing the same load, lower rpm would load the engine more..... Running at near max rpm, both my Yanmar 28 hp went bad prior to 3000 hours.... cracked pistons....
With what you have given, same boat, same prop, lower rpm pushes the boat through the water slower, so less force is required and less load on the engine. Overpropping your engine is a different story.

John
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Old 31-03-2009, 08:27   #9
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For my B series Cummins, they require them to be run at 100% for a half hour every ten hours. They say this keeps the carbon from building up. Getting the engines nice and hot does this.
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Old 31-03-2009, 09:46   #10
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I have two Yanmar 3GM30F engines in my catamaran for more than 15 years. I have 4500 hours on each engine, and I run them at 2200 to 2400 rpm when motoring, and at 1800 rpm when charging my batteries. So far I have had no problems with the engines. Only changes of water pump impellers, alternators, and exhaust elbows - plus routine maintenance.
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Old 31-03-2009, 11:42   #11
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i run my 3GM30F with 1400 hours to around 2500 and have had no issues. exhaust elbow is clear. 3000 seems a bit much when I go there but guess I should try it more often as Yanmar has suggested.
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