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Old 02-03-2020, 11:23 AM   #1
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White exhaust smoke on a prospective boat

Went to Nashville, TN this weekend with a friend to view a boat he is interested in. The boat is, overall, quite clean and move-in ready. We started the Cummins 6CTA engines and they produced a lot of white smoke with a very minimal, light sheen of unburned fuel on the water. The engines have about 2300 hours on them and appear to be well-maintained. They have been freshwater engines most of the 19 year life. Water temp was probably in the 40s and the air temp had been in the 40s but was at 60 when we started them. They started easily and ran very smoothly through 1800+ rpm. We ran them about 20 minutes and saw the temp gauges level out on Port at about 170 and Starboard about 160 (still rising). Toward the end, the smoke tapered off but was still a bit present. This is my first time looking at a boat outside of Florida.

I'm thinking cold water, cold/cool air temps, cold engines... fairly normal. During the survey, he will have the mechanic check the compression. Assuming it's okay (neither engine ran unevenly), is there some air heater function on the Cummins that might not have been working well? Clean the air separators and bring it back to Florida where the air and water are warmer. What do you folks think?

Also, there was a small air separator-looking thing on top of the hose coming from the main air separator. I haven't seen that before. Forgot to get a photo of it. What's that for?



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Old 02-03-2020, 11:34 AM   #2
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White smoke (unburned fuel) for up to 20-30 seconds on a cold start is normal. White smoke for 20 minutes is not normal.
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Old 02-03-2020, 11:55 AM   #3
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I had a pair of detroits that smoked quite a bit on cold starts. The smoke was not burned fuel but burnned oil -- the rings were shot. A rebuild solved that problem. What I "learned" at the time was there are three types of smoke -- black, white and blue. Black is unburned fuel -- often seen on diesel trucks under heavy acceleration, but even boats will often have a little brown (because there isn't enough to look black) smoke behind them while operating at cruising speed. White is steam, and dissipates quickly as the steam cools. Blue, which to me looks white with a barely perceptible blue tint is oil, generally from bad rings. When the engine heats up, the rings tighten up and the smoke diminishes greatly. The smoke in your second pic above looks
"blue" (ie, white with a slight blue tint) to me.
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Old 02-03-2020, 11:58 AM   #4
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My two cents, for what they are worth. I'm currently dealing with a little white smoke out my starboard engine, coincidentally also in Nashville. Different engines FL120, but possibly related cause. I forgot that I shut off my raw water intake while overnighting on the downtown dock. On the trip back I chewed up my starboard impeller. Replaced the impeller but ever since had the white smoke. After talking to the folks at American Diesel, was told I probably have rubber impeller bits scattered around my cooling system restricting water flow, which then causes the engines to run at an improper temperature, which causes the improper burn of the diesel, which causes the white smoke. I have spent quite a bit of time removing quite a bit of the rubber pieces. The white smoke is almost gone, except at very high rpms, so I'm making progress but obvious some more little buggers hiding somewhere.
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Old 02-03-2020, 12:07 PM   #5
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Greetings,
Mr. MV. The best way, IMO, to better diagnose/assess is to take the boat out for 15 minutes or so and run at some speed above idle. Letting it "warm up" at the dock doesn't do anything other than warm the coolant.
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Old 02-03-2020, 12:08 PM   #6
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Also for what it is worth, I happened to be at the boat this weekend as well. Started up the engines and let them run for about thirty minutes. FL120's tend to burn some blue smoke when starting and I happened to notice that this weekend they also smoked more than normal and left a little more sheen on the water than usual. I'm no expert but maybe it had something the do with the cold snap a couple weeks ago, got down to 18 or so for two night. I hadn't started them since before that cold came through.
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Old 02-03-2020, 12:24 PM   #7
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Methinks rings are worn . . . $$
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Old 02-03-2020, 01:24 PM   #8
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I have a Cummins 6CTA 450hp and when started with 40-50F sea water it does smoke like that. It is not burning oil or low compression, just cold intake air (via sea water after cooler). Cold intake air means the fuel does not burn completely. Some of the fuel comes out the exhaust as vapor.

The engine does come from the factory with intake air heaters, but some don't work and some are purposely disabled.

I would not worry about the cold smoke. Take the boat out and get engines under a load. Smoke should vanish then. After a run and tying up to the dock, the engine at hot idle should not smoke much. A little then is ok especially when sea (or river) water is cold.

No need to check compression. A blow by flow test is best to assess condition of rings.

Very robust engine. If it runs smooth and checks out ok you should be good to go.
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Old 02-04-2020, 07:02 PM   #9
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Dumb question by the uninformed: Would an oil analysis tell if the rings were worn?
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Old 02-04-2020, 07:12 PM   #10
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Quote:
Originally Posted by GFC View Post
Dumb question by the uninformed: Would an oil analysis tell if the rings were worn?
There could be some tell tales in the analysis, which he definitely plans to do.
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Old 02-05-2020, 08:25 AM   #11
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Quote:
Originally Posted by MV Wanderlust View Post
There could be some tell tales in the analysis, which he definitely plans to do.
There could be however if the engine was not warmed good when the sample was taken there could be a note like I had below on my recent analysis when I did not run the engine very much prior to the sample.

There is some fuel dilution, shown by the flashpoint temp, but that's harmless at
0.5%. Just starting the engine shortly before sampling could result in that level of fuel dilution.
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Old 02-05-2020, 08:41 AM   #12
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Are those the 450hp mechanical Cummins? It would be odd to have both of those engines rings and liners worn down that evenly at 2300 hours. I have seen cylinder heads removed from the same engines with much more time and there was still cross hatching at over 5000+ hours.
They are smokey engines at cold temps until they really get warm, And the only way is by running under load. The air box preheaters will show a load cycling on the volt meters as they kick on and off.
Fuel injectors may also be due for replacement and will clean the emissions up.
The headgaskets are known to fail with an external coolant leak when pushed to full throttle during a seatrial. I’ve also seen a few with failed valve seats that wreck a piston. There’s no way to tell when that might happen, but I’m guessing it’s statistically very rare.
Cold water and warm air temps already sets the stage for fog. Boat exhaust will enhance the conditions and you can have perfectly running engines that look smokey. My guess is these are somewhere in between.
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Old 02-05-2020, 10:14 AM   #13
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Thank you, everyone, for the insight. We're going back this Sunday for a survey and sea trial on Monday. Finding a marine diesel mechanic in Nashville is proving to be a challenge. We don't necessarily even need a written report from the mechanic.
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Old 02-05-2020, 10:37 AM   #14
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White smoke on a cold engine isnít necessarily a problem. On a warm engine under load white smoke could be a bad head gasket.
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