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Old 03-01-2011, 17:10   #1
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My Diesel Makes LOTS of Blue Smoke, but Does NOT Burn Oil - Is it My Injectors ?

I need advise, and was hoping you guys could help. I installed and maintained our engine, as well as built the boat, but this problem has me stumped! I have tried a LOT of solutions, to no avail...


The engine is a 16 year old 2 GM 20 F, with 2,400 hours on it. I have kept it pristine, and changed the oil every 100 hours. It is in a 34' Searunner trimaran.

It is slightly under propped, so easily reaches it's max RPM of 3,600.
(I cruise it @ 3,000 RPM)

It cranks and runs perfectly, with FULL power, and always has.

Although it used a normal amount of oil the first few years of its life... (I'd add 1/4 of a qt of oil every 20 hours or so)... for the last 10 years, it uses almost NONE!!! It might be 1/8" to 1/4" down on the stick, after the 100 hour oil change interval! (having added NO oil in that 100 hours)

My problem is that it makes a LOT of blue smoke at anything over 1,800 RPM! (NONE below that.) It is NEVER black or white smoke, and always while running like a champ.

I'm talking about an "abnormal" amount of blue smoke, although under way, one doesn't notice it much, because it is less smoke under load, and because the wind disperses and dilutes it. At the dock, she really belches it out!

I have tried everything I could think of, and followed a LOT of advise over the last 10 years...

The oil never becomes a different color, except darker, it never becomes less viscous, and never rises above the original "full" line. So the oil level staying almost full, can't be from diesel draining into the oil, (or water, as it does not become milky). It really doesn't use hardly any oil!

It is even when using "new" diesel fuel, with a cetane booster. A different source of fuel, or choice of oil, has had no effect.

I replaced the thermostat & confirmed with an IR thermometer, that she runs @ 180 degrees. So, it does not run too cool...

The only problem is the blue smoke... It cranks and runs perfectly. HOWEVER, I have never serviced the injectors. If the blue smoke is not coming from the standard problem of burning oil, can it be from burning too much diesel? (bad spray pattern).

Is it possible that servicing my injectors might fix the problem? Any other ideas?

Thanks!!! Mark
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Old 03-01-2011, 17:35   #2
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It only takes a very little bit of oil to make a lot of smoke.

On my larger yanmar the 'blow by' tube runs directly from the valve cover to the air intake. I can't make out if yours does from the pictures. If so, check where it enters the air filter and see if it is moist with oil.
When you run high rpms there is more presure in the crank case and more blowby will occur. Another thing that can contribute to more oil up in the valve cover is imropperly adjusted valves. Have they been done recently? How's the air filter itself?
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Old 03-01-2011, 17:37   #3
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While burning oil makes blue smoke so does incomplete combustion. Seems like you have no oil problem since the level won't drop. Air, spark, and fuel are what makes the engine go bang. What about the Air side of the fence? Over injection would be the other side of the problem. If you are not losing oil then it's not burning any oil would be something to take to the bank.

Injector service isn't something that expensive. How many engine hours do you have? You can't really do that job yourself and I wouldn't just swap them out on the idea that it was the problem. Being under proped isn't really ideal as it makes cavitation and increases the load with no performance gain.

I doubt the pictures of a clean engine will help. It does look really nice. I doubt it could be a problem. Loss of compression would be another source of the problem. A high pressure leak could be another.

Regular oil changes are just a good thing and you say you did them regularly so we can accept that. There is something more. You need to test some of the remaining possible problems.
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Old 03-01-2011, 17:40   #4
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2400 hours on the engine is a pretty good clue it's one or more of your injectors. Even if not, it's time to have them checked.
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Old 03-01-2011, 18:06   #5
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Thanks guys...

Good starting points from here... I have not seen much oil on the foam air filter next to the blowby tube.

The prop was under propped, so puts less load on the engine, but only by a hair. A lot of folks are propped so that the engine will not quite reach max RPM. Yanmar doesn't like this, so I made sure ours will.

No I haven't adjusted the valves in years, or serviced the injectors. I will do both!

Does the fact that my engine cranks instantly, idles smoothly, and runs with full power, with 100% reliability, mean that one or both of the above services is not it. Or either one could still be the problem?

Mark
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Old 03-01-2011, 18:42   #6
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Thanks guys...

Good starting points from here... I have not seen much oil on the foam air filter next to the blowby tube.

The prop was under propped, so puts less load on the engine, but only by a hair. A lot of folks are propped so that the engine will not quite reach max RPM. Yanmar doesn't like this, so I made sure ours will.

No I haven't adjusted the valves in years, or serviced the injectors. I will do both!

Does the fact that my engine cranks instantly, idles smoothly, and runs with full power, with 100% reliability, mean that one or both of the above services is not it. Or either one could still be the problem?

Mark
a 2GM should have a closed metal air filter. I doubt you would see oil on the foam easily.
Both service items should be done on a 1000 hr schedule.
I think the under proping may mask and decrease in power.
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Old 03-01-2011, 19:11   #7
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I've been told that blue smoke can be caused by worn rings and unburnt diesel.

Speculation from someone who knows nothing about engines:

My diesel will put out a fair amount of blue smoke on cold starts. As the engine heats up to normal temps it all but disappears. In the warm months there is virtually none... of very very little.

If this is related to the parts heating up and expanding and closing "gaps" such as piston rings it makes sense that the blue smoke is associated with unburnt diesel.

But what do I know????
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Old 03-01-2011, 20:15   #8
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The fact that it starts quickly with no smoke at start-up (other than that it always produces) indicates the valves are probably not the problem. Valves not properly adjusted would manifest itself in poor starting but, having said that, it is a generalization.
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Old 03-01-2011, 21:08   #9
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You could have a broken ring.

A compression / leakdown test of sorts may assist.
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Old 03-01-2011, 21:31   #10
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You could have a broken ring.

A compression / leakdown test of sorts may assist.
compression test will tell the story. After many years of dump trucks, heavy equipment and tractors I think you may be seeing the top ring beginning to wear out on a piston. If I recall correctly the 2gm should be somewhere around 350-400 psi for full combustion but will run as low as 200psi before unburnt diesel is shown as white smoke. Injectors are easy to remove to have shop bench test and adjust as necessary and you can do a compression test at same time.
Disclaimer: not a full time mechanic and dont forget to close raw water intake while turning motor over
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Old 03-01-2011, 22:00   #11
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On my latest naturally asperated diesel ('82 240D) I experienced excessive smoke when I first got it. It was black (which I associate with incomplete combustion) so I asumed injectors. My son had made a pop tester from a hydrolic jack and a guage so I pulled the injectors and they weren't far off. I shimmed them anyway and brought them up to specs with good spray pattern but it didn't fix the problem. Timed the injector pump and it was solved. Something you might do if it hasn't been done but if the smoke is blue, not showing up at low revs and the engine runs smooth it doesn't sound like fuel to me. On the the mercedes my oil level drops to it's place half way between the marks and stays there until oil change (5000 miles) but at high rev highway driving will smoke a bit and weep oil at the valve cover vent tube connection. Not enough to see on the dipstick but enough to see on the valve cover. It has 290,000 miles though...

If you goose it are you able to get a momentary blast of good healthy black smoke?

And one last thought ...for good health...what does the sniff test say it is? Diesel exhaust is pretty bad stuff but burning oil is pretty distinctive.
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Old 03-01-2011, 22:34   #12
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It sounds like you have done a thorough job of testing all possibilities. The fact that it starts immediately with no smoke pretty much eliminates the possibility of bad rings/low compression, along with the fact that the engine does not use any oil in 100 hrs. What is your fuel consumption rate (gal./hr), is it higher than normal for that engine at 3000 rpm? Since it's not using any oil I would think that the smoke has got to be coming from fuel and so the injectors should be tested and rebuilt/replaced as necessary. The engine has been doing this for 10 years and it hasn't changed at all in that time? Very strange.
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Old 04-01-2011, 01:32   #13
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I would also take a closer look a the piston rings. After I had a a top-end rebuild done on my Volvo (including reseating the valves), she blew lots of blue smoke for awhile because the new rings were still not fully bedded in. It was not an injector or valve issue.

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Old 04-01-2011, 06:48   #14
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To clarify some of the above...

I have left the problem alone for so long because it cranks and runs so well, and loaded up, underway, MOST of the smoke goes away, or so it seems. Yesterday... I did try a 2,500 RPM rev in place at my dock, (in gear), and it WAS still smoking... so I figured that underway, this reduced amount of blue smoke MIGHT be further reduced in appearance by being diluted from the wind, coming through the wing tunnel. (It is a Trimaran...)

Unless, with the cavitation created by running hard, "in place", is actually NOT much of a load. If that is the case, I haven't imagined it, and the engine really doesn't smoke under heavy load, while under way.

It only makes "black" smoke if I floor it suddenly to full 3,600 RPM, which I seldom do.

At my 3,000 RPM, cruising speed, I consume about .5 gal/hr, which is normal for this engine.

I did adjust the valves just after 1,000 hours, but now at 2,400, it is due again. I will remember... when turning over the engine without cranking, to close the raw water intake. (Thanks for the reminder)

I am not sure if that obnoxious smell is from blue diesel smoke or blue oil smoke???

My gut feeling is that with this incredibly low oil consumption, almost "0", and perfect cranking / running, it is just not burning oil... nor is it the rings, or valves. Although, I will adjust the valves, as they are due. It sounds like un burn't diesel to me.

#1, I will start by having the injectors rebuilt. #2, Then adjust the valves, #3, then do a compression check. It seems that if the injector timing was off, the cranking, running, and / or full power, would be off too?

I have been told by numerous mechanics, that @ 2,500 hours, my engine is just an adolescent. Nevertheless, if I have to pull the engine, I would "consider" having it rebuilt. I hate to resort to this though, as a rebuild cost $1,000 more than the engine did! (16 years ago)

They don't make these any more. Now it is replaced with the the 3-YM... This is a slightly larger, (better) engine, but would require a lot of modifications to get it to fit. On top of that, if I had that extra couple of HP, I would want one more notch of pitch in my prop, so I could use the extra power. (It is an $800 prop)!

So, even at $4,500 for a total rebuild, it is at least several thousand dollars cheaper than a new engine and prop, and WAY less work to reinstall.

With my current engine being so healthy otherwise, and so young, I hope it won't come to that!

Thanks for the feedback... Mark
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Old 04-01-2011, 06:58   #15
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The very simple answer is this,

Blue smoke = Burning oil
White smoke= Faulty injectors

Same with all Diesel engines the world over. Oil is getting into the combustion chambers somehow, I'd reccomend a compression test.
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