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Old 08-04-2012, 09:43   #1
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Yanmar 2gm 18 hp black exhust

I'm having a bit of a problem with my 2gm. Every time I run the engine for multiple hours at a time I always seam to get black soot all over my transom. I have wondered for a while weather the black soot on the transom is normal or not. I have a 1996 Hunter 29.5, the engine seam to run just fine with no power problems and throttle response seam to be fine. I'm just tired of having to scrub my transom every time I run the engine for more then 2 hours. The only thing I can think of is my aqua flow is clogged a little bit. Also my exhaust thur hull is under water, I don't know if that has any effect on it or not. Any suggestion with be appreciated.
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Old 08-04-2012, 10:04   #2
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Re: Yanmar 2gm 18 hp black exhust

I'm looking at page 73 - 74 in "Marine Diesel Engines" by Nigel Calder. He says that black smoke is the result of unburned fuel particles coming out of your exhaust. It's due to general "oldness" of the engine but the specific causes of are:
1 - Not enough air getting into the engine (Clean your air filter)
2 - Dirty fuel injectors not burning your fuel fully (Clean your injectors)
3 - High exhaust back pressure (more complicated)
4 - High ambient air temperature (increase the air flow into your engine compartment)
5 - Overloading the engine (prop too big, too much growth on the bottom, rope wrapped around prop, too many electrical things like refrigerators running on the engine)

I hope this helps. Keep us updated. I have a 2GM as well, so I'm very interested. Incidentally, the 2GM is only 13 horsepower continuous and 15 max, not 18.

Good luck,
Chris Ferro
Electrosense
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Old 08-04-2012, 10:18   #3
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Re: Yanmar 2gm 18 hp black exhust

Topsideup, if you tend to run your engine at full or nearly full throttle, try backing off a little(maybe 200 revs) and see if it still does it. All of the things mentioned in the last post are good, but maybe just not running the beast so hard could change things. That is a try that doesnt cost anything. Good Luck._____Grant.
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Old 08-04-2012, 10:27   #4
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Re: Yanmar 2gm 18 hp black exhust

And also check the exhaust elbow for plugging which restricts exhaust flow. This is a chronic problem on the gm engines. Seems to start at about 1000 hours.

You can pull off the water injection hose and look inside. Sometimes you can see or feel a restriction, sometimes not.

David
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Old 08-04-2012, 10:30   #5
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Re: Yanmar 2gm 18 hp black exhust

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Topsideup, if you tend to run your engine at full or nearly full throttle, try backing off a little(maybe 200 revs) and see if it still does it. All of the things mentioned in the last post are good, but maybe just not running the beast so hard could change things. That is a try that doesnt cost anything. Good Luck._____Grant.
I have thought of this and yes I do run it a bit hard from time to time. I have noticed tho that I still get black soot on the transom when I'm running around 2400 rpm. When I made my passage from Sand key to Luperon I ran the engine for 5 hours and never above 2000 rpm and still had black soot on transom. this has been a ongoing problem since I left Boot Key harbor in Dec. .
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Old 08-04-2012, 10:58   #6
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Re: Yanmar 2gm 18 hp black exhust

As said above ! Ya need a TUNE up soot is a sign of a fuel problem, improper fuel amount, more than likely your injectors are over time for cleaning and resetting. Maybe a compression ck cus worn rings, valve stem seals can cause the same problem! might be time for a ck up!! Hope ya know a diesel guy who might help ya out! I would be glad to help if yall come down my way ! Just my 2 cents
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Old 08-04-2012, 22:21   #7
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Re: Yanmar 2gm 18 hp black exhust

First...have the injectors serviced.....make sure your mechanic doesn't try to re-use the injector seat washers or the crush washers.

Before you do all that check the bottom and prop
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Old 09-04-2012, 09:00   #8
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Re: Yanmar 2gm 18 hp black exhust

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And also check the exhaust elbow for plugging which restricts exhaust flow. This is a chronic problem on the gm engines. Seems to start at about 1000 hours.

You can pull off the water injection hose and look inside. Sometimes you can see or feel a restriction, sometimes not.

David

The mixing elbow was replaced about a year ago. Also the boat just got a bottom job a little over a week ago and is clean as a babies bottom. It looks like I'm leaning toward injector service.
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Old 09-04-2012, 09:41   #9
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Re: Yanmar 2gm 18 hp black exhust

While the injectors are out you might want to do a compression check, just to check on the general condition of the engine.______Grant.
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Old 09-04-2012, 10:06   #10
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Re: Yanmar 2gm 18 hp black exhust

I agree with Chief Engineer, I had the exact same problem a couple of months ago, I had my injectors cleaned and rebuilt, along with the injector pump and everything is AOK now. I do not think the injector pump was the problem, I do think it was the injectors themselfs, But the engine had 5000 plus hours and I felt the pump needed service to. Be sure to reinstall all new washers and get the injector seat clean before reinstalling the clean or rebuilt injectors or you will have leak problems, don't ask me how I know that.
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Old 09-04-2012, 10:09   #11
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Re: Yanmar 2gm 18 hp black exhust

I dont know if I've ever had a diesel that didnt accumulate some black soot on the boat near the outlet. Some were much worse than others due tothe exit location and stern shape. The exhaust was always clean looking, but over time accumulated on the boat....
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