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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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  #1  
Old 08-17-2013
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Yanmar 2QM20 Smoke Opinions?

I'm troubleshooting my Yanmar 2QM20. The engine has gotten air in the lines once each of the past three seasons. Each time I think I found the leak and fixed it. This last time was a month ago motoring into our river head on in some strong winds after about 10 minutes, the engine died. I successfully sailed into our slip for the first time and troubleshooted the engine the following weekend. The engine fired up, but soon stalled. I'm pretty sure it was air getting in the lines somewhere. I found a hairline crack in the surface of one fuel line, between the tank and primary filter. I replaced it and checked every connection for any possible air getting in. After bleeding the lines, I ran her in gear for 20-30 minutes in our slip. She ran great, without a hiccup. I'm hoping that line replacement was the fix.

Now, my main question has to do with I've always noticed the engine has a small amount of smoke. It is hard to tell if it is white or blue. Here is a video I took while under load in the slip:
I've read online and in my diesel engine book about what colors of smoke mean and white and blue don't sound good. Here is a site I've come across: Diesel Smoke tells YOU a Story…
I'm guessing I have good compression because the engine usually fires up quickly. There are no glow plugs and in cold fall weather, I remove compression, spin up the engine a couple seconds, then engage compression and she fires up. Having the right tools or a mechanic check would give me a better idea.

Does anyone have opinions on the smoke in this video? Should I be concerned or is it typical for these old engines to put out this amount of white/blue smoke regularly? I don't want to end up having to invest in a new engine anytime soon, actually ever while I own this boat. I'm also not sure what the replacement part supply is like with these old Yanmars.

Thanks, now time to go sailing!
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Last edited by JustinC25; 08-17-2013 at 11:29 AM.
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Old 08-17-2013
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Re: Yanmar 2QM20 Smoke Opinions?

Is it burning oil? If fwc does it lose fluid?
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Old 08-17-2013
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Re: Yanmar 2QM20 Smoke Opinions?

I checked the oil and it appears to be where I filled it to when I changed it. I've probably only put a few hours (<10 guessing) on the engine this season, so I guess depends on the rate it burns, if the engine doesn't get used much, I won't see much oil lost. It is raw water cooled.
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Old 08-17-2013
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Re: Yanmar 2QM20 Smoke Opinions?

Quote:
Originally Posted by JustinC25 View Post
I checked the oil and it appears to be where I filled it to when I changed it. I've probably only put a few hours (<10 guessing) on the engine this season, so I guess depends on the rate it burns, if the engine doesn't get used much, I won't see much oil lost. It is raw water cooled.
If you take it out and run it hard for an hour or so does it still smoke?

Can you get to maximum specified RPM in gear, under way? If not, the prop may be dirty or over pitched, which may cause some smoking. Kind of hard to tell from the video, but the smoke didn't look that severe. If you are not burning much oil, and it is timed properly, the injectors may need to be re-built or replaced.?

If the fuel is really old that might be part of it although that may be a stretch.

Any restriction in the air induction tract, dead things, or dirty air filter, if it has one?

Paul T
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Old 08-18-2013
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Re: Yanmar 2QM20 Smoke Opinions?

If these run at low RPM for extended times, they will develop glazed cylinder walls and start burning oil. It's best to run them at 2600-2800 RPM most of the time so this doesn't happen. Also, if the engine has sat for a LONG time (as in years) the rings will lose effectiveness. I wound up doing a ring job on my 3GM which sat for 6 years. The motor only had 70 hours on it.
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Old 08-18-2013
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Re: Yanmar 2QM20 Smoke Opinions?

Yesterday was a great day on the water. I ran the engine for the first 30 minutes motoring us 5.5-6 knots into a 10 knot breeze. There was no smoke that I could see, but the wind could have quickly dispersed the small amount of smoke that I had while stationary in our calm slip. On the other hand, there was no smoke during the ~10 minutes of idle while we prepared to head out and no smoke when we returned. I let the engine idle for 5 min or so and then revved her up for several seconds just before shut down. I never saw any smoke. I have seen smoke in the past while out on the water, but not every time and I recall it being on calmer days. That video above was from the last time I used the boat prior to yesterday, so it is odd that I did not see any smoke.

The prop should be clean. I sprayed anti-growth paint on it when we launched this spring. Last year I dove and checked the prop which had been underwater for over a year without any of the paint, and it barely had any growth on it. It is a 3 blade prop. I don't think it is over propped, but although I don't know for sure.

Fuel is relatively fresh. A new tank was installed when I bought the boat 2.5 years ago and it is a 12 gallon plastic tank. There is no visible growth and the filters are good. Air filter is good, no restrictions there.

Unfortunately the engine does not have any gauges. I am thinking about installing them. They would give me some piece of mind having a better idea of what is going on. Instead, for now I just stay really in tune with the engine, always listening for any changes in sound, checking exhaust, and running her at a smooth higher RPM. I wish I knew what RPM I'm running it, but I usually target 5-6 knot range in med-light conditions. I've known it's best to run diesels at their 80% capacity range, so I try to avoid idle and low speed. The engine has 2400+ hours on it over 35 years, so I have no idea about its history though. Before I bought the boat, I was concerned about the amount of hours, but I found, like smurphny said, very low hours can mean even more problems.

It is odd that the smoke is inconsistent. Can smoke be from a tiny bit of air still in the lines, but not enough to stall? I bled the lines until no bubbles came out, so I would not think that is the case. I'm going to keep monitoring the engine and exhaust whenever I use it. I might go ahead and buy the proper Yanmar tachometer and install it. The transmission housing has a plug where the tach connects, rather than calibrating one to use off the alternator.
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Old 08-18-2013
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Re: Yanmar 2QM20 Smoke Opinions?

Without a tachometer, it's very possible you've been running at too low an RPM. There's really no way to determine by sound. In fact, these sound really comfortable at 2000 RPM. If you've been running at low RPM there is a possibility that some glazing has occurred and some oil is slipping past the rings. At hull speed, you should ideally be running at around 2600 or so (from 3GM30 specs) or wherever your peak efficiency is on that motor. You can find your torque curves in the service manual.
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Old 08-18-2013
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Re: Yanmar 2QM20 Smoke Opinions?

Yeah, I would feel much better knowing what RPM I've been running. I came across the Tiny-Tach Design Technology, Inc., Home of the Tiny-Tach - Diesel Tiny-Tach Tachometer and have read lots of good feedback. It looks like a simple installation. I read on another forum that someone was looking for the Yanmar tach for their 2QM20H and their dealer said it isn't made anymore.
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Old 08-18-2013
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Re: Yanmar 2QM20 Smoke Opinions?

Give Mack Boring a call. I think Yanmar panels are still available but, I would imagine, wickedly expensive. You'd probably be better off with an aftermarket product. I have a type B panel and have seen replacements for sale. Sometimes you see them on EBay when people upgrade to the C type. There is also a Yanmar aftermarket panel on EBay that has actual gauges instead of idiot lights. That little unit you linked to looks like it would do the job.
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Old 08-19-2013
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Re: Yanmar 2QM20 Smoke Opinions?

The crankcase breather tube may have a spot where vapors condense and leave some oil to be accumulated, which may be drawn into the intake air stream, causing it to smoke a bit from time to time?

Maybe the valve guides are a bit worn, allowing some oil to be pulled into the intake stream. I think most diesels do not have a throttle plate, as gas engines do, so there may not be that much vacuum in the intake tract to do that?

In any event, it sounds like it is running OK without too much smoke? It would be handy to have a tach, so you can run it at proper RPM's.

Paul T
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