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Old 05-25-2020, 06:38 PM   #1
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Grey exhaust smoke at 9+ kts

We took the boat out for our shakedown cruise today. Everything was fine until I got the boat up to 9.5ktx which is when I noticed grey smoke coming from the exhaust. It went away as soon as I slowed down. Quick internet search indicated possible fuel injector, fuel filter and some other options. Wanted to reach out to see what folks on the forum would suggest? Engine is a 350 Yanmar.

Thanks in advance for your input.
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Old 05-25-2020, 07:00 PM   #2
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Is it smoke or steam? What temp was the engine running at?

If temp is normal it's time to look at the injectors.

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Old 05-25-2020, 07:05 PM   #3
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I doubt that smoke from fuel would go away that easily. Steam may.

Steam while present will dissipate fairly quickly, smoke will not and if from fuel will be very persistent and strong smelling.

Most likely you have a lack of raw water flow problem.

I've tossed my tome in below. Read it through and if there are questions ask.
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Old 05-25-2020, 07:15 PM   #4
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Pete we were running at about 175 which is what we always do.
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Old 05-25-2020, 07:22 PM   #5
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I had not thought about steam, it did seem to disipate quickly and I did not notice a smell. Thanks for sending your doc, I am going to check what I can tomorrow and then likely have the mechanic swing by.
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Old 05-25-2020, 07:56 PM   #6
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Pete we were running at about 175 which is what we always do.
You can have enough raw water to keep the engine at proper temperature, but not enough to keep it from vaporizing in the exhaust elbow.

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Old 05-25-2020, 08:06 PM   #7
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Old 05-25-2020, 08:39 PM   #8
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You can have enough raw water to keep the engine at proper temperature, but not enough to keep it from vaporizing in the exhaust elbow.

Ted
I second this. If total water flow through the system is a bit low, everything will seem ok but the lesser amount of water in the exhaust will cause that water to be vaporized more. Itís a fairly common problem.

Ken
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Old 05-25-2020, 08:53 PM   #9
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Is this a new to you boat? If so, some engines and exhaust systems just steam a bit under load. So I'd still check everything over, but if you don't find anything wrong, it could be normal.
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Old 05-25-2020, 09:24 PM   #10
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Year 5 so it raised a flag
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Old 05-25-2020, 10:13 PM   #11
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I'd check the exhaust temps. I had a problem a few years ago when my exhaust spray deteriorated, enough water was going through but it was a stream, not a spray. Under load the exhaust would overheat, eventually causing failure of the rubber hose. We had to re-build the spray system.
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Old 05-25-2020, 10:16 PM   #12
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Re prop lately?
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Old 05-25-2020, 11:21 PM   #13
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White smoke is normally unburned diesel or water/coolant.

At the slip, especially on a calm day, it is usually easy to tell one from the other. Water vapor tends to float away. Diesel tends to linger. Diesel may slick the water. Water does not. Water vapor usually has no real smell. If it has any smell, it is a sweetness, which is bad, as it is antifreeze. Diesel has a distinct miserable taste, smell, and even eye feel if there is enough.

Underway, it is harder to tell unburned diesel from water vapor as one is moving away from it, spreading it out. But, if one does see it linger, it is unburned diesel.

Blackness in smoke is partially burned diesel. It is the result of the engine not getting enough oxygen to fully burn the fuel. In a diesel this can be normal while accelerating as the fuel is supplied first, then the RPMs go up, getting in more air. So, there isn't enough air until the RPMs catch the fuel.

If there is a turbo (and I think you may have twin turbos!) , and it isnt working, at the point of the fuel curve where it should be pushing in more air, if it doesn't, smoke with grey up and turn black. It is also caused by overloading as it prevents the engines from developing the RPMs to match the fuel curve, so not enough air gets in.

Overloading can be caused by a dirty bottom, fouled props, over propping, or an engine that just isn't generating as much compression as when it was new so can't handle the same load, or a turbo not boosting.

Blue smoke looks a lot like black smoke. It is a blue black. It is from motor oil in the exhaust. If it is sudden or a short ramp up to the problem in a turbo engine, it could be a turbo leaking. It could also be something worse. If it increased slowly over time, it could just be age....aging rings or valve seals. Depending on how bad, it could be like some grey hair -- nothing more than a sign of midlife. This usually isn't super load sensitive. Rings tend to improve as things warm up and seal better. Valve seals might, or might be more intermittent.

Grey smoke tends to be a mix of white smoke and black or blue smoke.

If the engine is losing oil....that is another sign of an oil leak. If it is losing coolant, a coolant loop leak, often a head gasket. If the oil is milky, that might be water getting in, such as from a cooler or head gasket leak. If oil is getting thinned out, especially if fuel is getting in, that is a sign of fuel getting in, such as worn rings and excessive blow by.

Since the smoke being reported as grey and under load under way, I'm more concerned about the black component that the white component, if for no other reason that white smoke underway that doesn't occur at the slip is almost always steam -- underfunded fuel tends to get better underway, or at least more spread out.

So, focusing on the black part of the grey. Get the diver to clean the bottom and check the props. Check the oil level and character. Check the coolant level and character. At the slip with the engine running, pull the valve cover oil fill and feel for excessive blow by. If, and only if, you know how to do it confidently and safely, pull the coolant cap and look for exhaust gas leaks. Check the turbos to make sure they spin freely. While underway get someone in the cabin or engine room close enough to hear the engines well. Is any turbo making crazy noises? Compare unfamiliar things like the sound and blow by from one engine to the other.

There is obviously a ton of other places to look, but I'd suggest starting here...it is free stuff to check...and then reporting back. With more info you'll get more ideas from the peanut gallery!

Good luck!
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Old 05-26-2020, 06:39 AM   #14
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Air Filter
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Old 05-26-2020, 06:50 AM   #15
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Air Filter
Oh! True that
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Old 05-26-2020, 07:51 AM   #16
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Fuel filter would be the first thing I check, especially with this being a shake down cruise after sitting for a while.
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Old 05-26-2020, 07:57 AM   #17
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If it was my boat I would open, inspect and clean the entire raw water cooling system
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Old 05-26-2020, 01:17 PM   #18
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Thanks all, I am meeting the mechanic there tomororw or Thursday and will get insight into the issue. The way the winds have been yesterday was the first day we could go out, hopefully this issue is minor and the weather start to change. Otherwise there will be a lot of dock time.
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Old 05-26-2020, 10:08 PM   #19
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Restricted aftercooler denies motor of air too, usually gets clogged up when too much oil is coming out of the crankcase.
Poor turbo performance starves motor of air, especially at higher rpms, you may want to pull off the exhaust elbow and take a peek inside the turbos exhaust exit side, or at least insure that it spins freely from the air intake side.
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Old 05-27-2020, 09:07 AM   #20
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Restricted aftercooler denies motor of air too, usually gets clogged up when too much oil is coming out of the crankcase.
Poor turbo performance starves motor of air, especially at higher rpms, you may want to pull off the exhaust elbow and take a peek inside the turbos exhaust exit side, or at least insure that it spins freely from the air intake side.
A failed turbo will cause lots of black smoke, too much fuel and not enough air. White/grayish smoke is too much air, not enough fuel.
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