Yanmar 3GM30F - Page 2 - SailNet Community
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post #11 of 31 Old 09-26-2007
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I have the same engine. If remember correctly in the manual on the 3GM30F the recommended continuous operation is 2800 RPM and that is the RPM that I run my engine.
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post #12 of 31 Old 09-26-2007
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might have missed this - but did you test the Thermostat?

Rick

quote=Bill Mc;198391]Prop is original size and pitch and clean, no barnacles.
Fresh water cooled engine, so no internal zincs.
Impeller is fresh, Just replaced by yours truley so I know at least this is right.
Only smokes a little when started after a week long layup, this has been improving since the marina in their infinite wisdom used EITHER to get her cranked to do my bottom job. ** I will no longer beat that dead horse}.
I believe we were doing about 6 kts at 3100 rpm and 5.3 kts at 2250 rpm.
70% = 2520 rpm, 80% = 2880 rpm, 86% = 3100 3100 = BAD???

So I'm still scratching my head on this one. Thank ya'll for the feedback. I'll get this figgered out if it kills me. Financially that is...

Fair Winds,

Bill[/quote]
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post #13 of 31 Old 09-26-2007
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Quote:
Originally Posted by sailvi767 View Post
. Running a diesel long term at lower RPM's (under about 80%) leads to wet stacking which is very harmful to the engine.
Can I ask a stupid question? What is wet stacking?
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post #14 of 31 Old 09-26-2007
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A diesel engine is subject to "wet stacking" or over fueling if run for long periods of time with ultra light loads (less than 40% of the rated output). "Wet Stacking" causes the engine to smoke and run rough because the injectors become carbonized. Running a heavy load will usually clean up the over-fuel condition and allow the engine to perform properly. Diesel engines operate better and more fuel efficient when loaded (70-80% of the rated output is optimum). Source: http://www.allworlddieselgen.com/faq.htm

This condition happens to a lot of cruising boats who rely on running their main engine to charge their house battery bank while at anchor. I would also note that other experts say this can happen at higher loads than 40% and that cruising at 80-90% of rated RPM's is best. Main thing is to cruise at least at 70% RPM's and don't run your engine while atanchor to charge batteries!
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post #15 of 31 Old 09-26-2007
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Our 3GM30F is rated as follows:

- 27hp @ 3600 rpm for one hour
- 24hp @ 3400 rpm continuous

I have always assumed the recommendation to run at 80% rated power was referring to the continuous rating, yielding 2720 rpm. We run ours between 2700-2800.
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post #16 of 31 Old 09-26-2007
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Somebody please help me on this but I believe the problem could be that the shaft is to tight and needs to be loosend. The water needs to be dripping a certain rate every minute. The same problem has occured on my Island Packet with the same engine.
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post #17 of 31 Old 09-27-2007
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If the shaft gland were over-tight, and causing a drag on the shaft, it would absolutely fry. The heat build-up would be overwhelming and would risk twisting off the stuffing box assy.

I don't think it is that!
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post #18 of 31 Old 09-27-2007
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The answer is simple, back off the packing gland nut a small amount. There typically is a locking nut and the packing gland nut, and a nut shaped casting on the end of the packing gland itself. You need to be able to hold the packing gland nut with one wrench to keep from twisting the packing gland while loosening the locknut with another wrench. Then you need to hold the nut shaped casting with one wrench while loosening the packing gland nut with a second wrench. I would loosen the packing gland nut roughly an eighth turn, and lock down the locknut again. The packing gland should not leak when the engine if off. There are various opinions on how much water should leak out when the shaft is turning and some of that is dependent on material used for packing. I haven't had a packing gland on one of my boats for over 25 years but if I remember correctly they used to say, 1 drip per minute.

Jeff
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post #19 of 31 Old 09-27-2007
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151 Fix

Just apply generous amounts of 151 Rum until the problem ino longer becomes a concern.

Warning!! This is only a temporary solution and may require multiple applications.
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post #20 of 31 Old 09-27-2007
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Even if the drag on the shaft was the equivalent of 1 hp, the local heating would be about 700 Watts and it would steam, and steam and steam.

If in doubt, slack off the packing and see if it improves. Whatever you do, do not over-tighten it. Let it drip a little. It does no harm.
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