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Old 07-14-2019, 10:10 PM   #1
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City: Dodgeville, Wi
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Yanmar UTE question ...

Well, I could sure use some advise. My engine is a Yanmar 4JH2-UTE. I have a 2.63:1 gear reduction swinging a 4 blade 20x18 wheel( pretty sure on prop ). This is on a semi displacement New England style pick nick type boat, 25 feet long, dry weight 6400 pounds, loaded around 8000 with passengers, gear and fuel.

A month ago or so I had a survey and the tach reached 3600, and 12 knots at 2900 rpm. That is on spec, however, low fuel, no water, minimal gear and two adults.

When I picked it up, it over heated,Florid water and weather much warmer after survey. We flushed the raw water side and found the thermostat missing. We replaced with a 173 degree thermostat from Yanmar. Boating in the cooler Mississippi River, the motor sits at about 85 degree C all day.

However, it used to grey black smoke at about 2600 rpm or higher, the more RPM the more smoke. At the dock, after running the river, idling down, I would raise RPM a few times and soot would float out exhaust. Now after about 45 hours of running up and down River 2600 to 3000, and using diesel kleen there is almost no smoke, gotta really look hard to see it and only after 3100 PRMs.

However, My load is my wife and I plus two 60 pound plus dogs, 2 coolers, gear for 4 days trips plus 60 gallons of fuel and 10 to 20 gallons of water. When traveling up or down current, I can only manage 3450RPMS.

I Have wondered if may be I have a sticky injector, or may be over propped a bit ... or something else? Down river, with load above at 2900 RPM I do about 10.5 knots, up river it is like 7.5 knots ...not 12 like during the survey. Is this likely do to the load or maybe is something wrong from the overheating?

I look forward to any and all replies as I really love the boat and do not want to hurt the engine.
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Old 07-15-2019, 06:37 AM   #2
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As currently loaded you can only make 3.450 rpms and rated is 3,600, right? Then you are over propped and that is what is causing the smoke. Talk to a good prop shop about taking about 2" out of your pitch.


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Old 07-15-2019, 08:41 AM   #3
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I think that thing is rated for 3800, but not 100% sure. Engine tag should show rated rpm, go look at your tag. Want full power rpm to be a little above that, say 3850-3900. If propped for 3600, you have too much prop, and it will smoke.
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Old 07-15-2019, 09:22 AM   #4
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Yup, continuous rated for 3400 rpm, max 3600 rpm. I prefer to run at about 2700, but will like to hit 2900 to 3000 when running up current. At those rpms, I do see a hint of smoke, almost not there, but I believe there should not be any smoke. I appreciate the replies. If I am slightly over propped for my weight, am I hurting the engine if I do not make a prop correction before fall winterizing?
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Old 07-15-2019, 10:28 AM   #5
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Keep it at 2,900 or less and you should be fine until fall. And don't believe Yanmar's continuous rating. Even when propped right stay 400 rpm off of top.


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