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Old 30-06-2020, 16:09   #1
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White and Offensive.. Diesel Smoke Diagnosis

Diesel smoke diagnosis isn’t anything new on the forum but I’m hoping this will help owners of older, raw water diesels from panicking.. in my case, it’s an Md7a.

Most use is less than 30 minutes at a time and stays below 2000 RPMs, so overheating doesn’t seem to be a factor. Given the immediate startup and reliable power, water intrusion or terrible compression don’t seem to be factors either. Exhaust elbow looks quite rusty on the outside, could a partially blocked exhaust or muffler be causing consistent smoke and perhaps the rusty water? Does this simply sound like textbook injector failure?

The good:
- Starts within 1 second every time (electric starter)
- Delivers reliable power (thrust)
- Appears to not overheat

The concern:
- Consistent white smoke from startup thru operation (enough to be obnoxious at the dock)
- Rust colored exhaust water for the first 3-5 mins of running
- Diesel sheen in the exhaust water (hard to notice unless the water is dead still)
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Old 30-06-2020, 16:25   #2
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Re: White and Offensive.. Diesel Smoke Diagnosis

given the current times, interesting choice of title

I would start by giving the engine a loaded run up to temperature and then going full throttle for a few minutes, back back down to 2000 rpm, then repeat a few times.

My engine loves the short full throttle bursts every few hours to blow out.
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Old 30-06-2020, 16:51   #3
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Re: White and Offensive.. Diesel Smoke Diagnosis

Could help. Thanks, sailorboy1. Engine has less than 10 hours this season still. New oil and an entirely new tank of fuel. (Drained the tank)
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Old 30-06-2020, 17:35   #4
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Re: White and Offensive.. Diesel Smoke Diagnosis

If it’s whitish smoke that stinks and doesn’t dissipate quickly like steam would, it’s most likely unburnt fuel, most probably from a worn / varnished up injector.
For an example look up YouTube for cold start Diesel or similar.

The Diesel sheen also adds credence to a malfunctioning injector, pull them and take them to a Diesel injection shop, many think they can service their own injectors, but it’s very unlikely the have the tools to do so, for starters you need to determine the cracking pressure of the injectors, not just the spray pattern.
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Old 30-06-2020, 18:59   #5
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Re: White and Offensive.. Diesel Smoke Diagnosis

Can you post a video? Makes it easier to see exactly what smoke is like but yes could well be injector. When did you last check exhaust elbow for clogging? If its been a few hundred hours would pay to check anyway.
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Old 01-07-2020, 04:07   #6
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Re: White and Offensive.. Diesel Smoke Diagnosis

Thanks for the reply. Got to check out the exhaust elbow then. I know it’s been a while. I don’t think the previous owner paid much attention. Here’s a little GIF video of about two minutes after cold start. The amount of white smoke is pretty much unchanged even after running for let’s say 20 minutes with load and getting up to temp.



https://imgur.com/gallery/5aCvcwY
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Old 01-07-2020, 09:56   #7
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Re: White and Offensive.. Diesel Smoke Diagnosis

Does the engine rev as well as it used to?
I had to replace the exhaust elbow on a D2-40 after 800 hours that was completely blocked. Initial symptoms were loss of revs both in neutral and, very noticeably, in gear resulting in loss of thrust, plus the evil smelling exhaust.
It rapidly deteriorated over the next couple of runs until there was also a serious diesel knock. My engineer thought it was fuel related (injectors, pump, compression) but it was the blocked elbow. It causes exhaust gas to not be properly purged from the cylinders and then unburnt diesel causes pre ignition (knock) and the smelly exhaust.
I would check the elbow (free) before getting the injectors checked ($$$).
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Old 01-07-2020, 09:58   #8
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Re: White and Offensive.. Diesel Smoke Diagnosis

Excellent tip. Will give it a shot and post the result
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Old 01-07-2020, 10:19   #9
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Re: White and Offensive.. Diesel Smoke Diagnosis

Looks like unburnt fuel. Try Liqui Moly Diesel Purge as a first step. If that doesn't work pull the injectors and have them rebuilt. Check your compression when you have the injectors out.
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Old 01-07-2020, 12:54   #10
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Re: White and Offensive.. Diesel Smoke Diagnosis

White smoke, which is normally water vapor, is a sign of water getting near or into the combustion chamber. Or perhaps water entering into the hot part of the exhaust elbow. As is rust coming out of the exhaust. If your cooling water volume has been greatly reduced this can cause white smoke /steam as well.
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Old 01-07-2020, 15:45   #11
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Re: White and Offensive.. Diesel Smoke Diagnosis

Quote:
Originally Posted by JacoLTD View Post
Diesel smoke diagnosis isnít anything new on the forum but Iím hoping this will help owners of older, raw water diesels from panicking.. in my case, itís an Md7a.

The concern:
- Consistent white smoke from startup thru operation (enough to be obnoxious at the dock)
- Rust colored exhaust water for the first 3-5 mins of running
- Diesel sheen in the exhaust water (hard to notice unless the water is dead still)
Rust colored water is usually a cracked manifold... sits for some time and water and rust and lays in bottom of manifold... upon startup... water turns into steam and the rust is purged out through the exhaust... Let us know what you find please... Thanks... Good luck in you search...
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Old 01-07-2020, 16:57   #12
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Re: White and Offensive.. Diesel Smoke Diagnosis

Had a similar problem with my (new to me) but older Yanmar 3gm, heading out from anchorage on a coolish morning giving it some high throttle to head into wind, belching clouds of white smoke billowed out, I almost turned back but decided to throttle down and wait and in 10 mins it warmed up and smoke disappeared. I know now to warm it up and be light on the throttle. Perhaps take it for a good run to clear it out.
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Old 01-07-2020, 18:22   #13
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Re: White and Offensive.. Diesel Smoke Diagnosis

Looking at your video I suspect there is a fair bit of steam in the smoke. It's more obvious further back in smoke trail if it's steam rather than smoke but in the vid I could only see the plume close to the tailpipe. The rust in the exhaust leans towards post 10 or 11 fault finding so I'd check the elbow before the injectors tho they could be faulty as well but 1 thing at a time.
Post back what you find please.
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Old 02-07-2020, 14:39   #14
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Re: White and Offensive.. Diesel Smoke Diagnosis

White smoke is unburned fuel. Sticking valve, blown head gasket (could also explain water) damaged piston all come to mind--my guess is gasket or sticky exhaust valve.
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Old 02-07-2020, 14:55   #15
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Re: White and Offensive.. Diesel Smoke Diagnosis

Great inputs. Thank you all. Obviously an old engine, so itís just a matter of time. Definitely no steam action. This video is from two minutes after start upÖ not even the oil is warmed up. Plus this is a raw water cooled engine, so if seawater was getting into the cylinders, this thing would be hydrolocked after a week of no use. Going to rule out head gasket because the oil is perfect. Going to rule out the sticky exhaust valve because thereís zero hesitation with the RPMs and power.

I think the rust is from an aged exhaust manifold/muffler and the smoke is from the exhaust elbow and/or injectors.

Going to start with running the engine a healthy amount of time at increased RPMs. Then a removal of the exhaust riser. If it doesnít solve the smoke, itís the injectors and that will have to wait until winterÖ Or maybe just live with it.
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