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White smoke in exhaust-Yanmar diesel

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Apr 20, 2010
119
Hunter 34 San Mateo
Is white smoke a bad thing? I have a 1983 Hunter '34 with a Yanmar diesel. At low rpm under load I'm OK. At around 2000 rpm under load, I get some white smoke. Some other people with older boats tell me it's normal for their boats. I checked my oil level and it's fine. What do you think? Thanks.

--Dan
 
May 25, 2004
420
Catalina 400 mkII Harbor
i had a similar issue, a yanmar mechanic told me to go out and run the engine for 15 minutes at full load. it did the trick no more smoke. he mention something about cylinder walls.

mike
 

Ivan

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May 17, 2004
234
Hunter 356 Solomons MD
Run at full load

That's right. All marine diesel engines should be run at full speed and full load for 30-60 minutes every few weeks to prevent the cylinders from getting glazed. Glazing happens when the engines are run slowly or at low load, which is typical of how auxiliary diesels are used in pleasure boats. You want to avoid glazing, which would cost thousands of dollars in repairs--and costs nothing to avoid.

BTW: That also applies to diesel generators, which should also not be run without at least the minimum manufacturer's wattage load for the same reasons (the minimum is 1/3 of the rated maximum load in my Fischer Panda).
 
Dec 2, 1999
15,184
Hunter Vision-36 Rio Vista, CA.
Dan:

Are you sure that it is not blue smoke vs. white. I think if you check the archives white smoke indicates water (things like head gaskets, moisture in the cylinders etc). Be sure to check your coolant level and your oil. If the coolant is lower then you can have a head leak (warped head, blown head gasket). There can also be signs of water getting into the crank case and the oil will start looking "milky".

You may also want to be sure that your fuel filters are clean too.

Best of luck, be sure to keep us informed on what you find.

I would agree that you should be running your engine at higher RPM's if you are not doing this. You engine is rated at 3600 RPM's. If you have the correct prop you should be running it at 2600--2900 when at cruising speed.
 
Feb 6, 2009
257
Hunter 40 Camano Island
Diesels need to be loaded, and they are delivering there power through a prop. I am out of town and away from my manuals, but Typically on those small yanmars... 75% load (recommended by most yanmar diesel mechanics as the minimum for extended cruising ) is about 2900 RPM, and most prefer 80% power output for engine load, around 3000 rpm for that engine. I will check the torque, prop curves when I get back.
 

BillyK

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Jan 24, 2010
502
Catalina 310 Ocean City, NJ
Is it steam? Could have a dirty heat exchanger making it work hard and produce steam....
 

Ivan

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May 17, 2004
234
Hunter 356 Solomons MD
Billy K:

You have raised a good point: Steam is definitely a possibility when you see white exhaust. However heat exchangers don't "work hard" in the human sense. But if they are partially clogged the coolant temperature may increase substantially because of inadequate cooling and so would the heat exchanger temperature, and then steam formation would be a possibility. Also if the cooling water flow is reduced it could be turned into steam in the exhaust elbow since it also would be running hotter than designed.

Yes, steam is defintely a possibility, and if none of the conditions that Steve Dion has mentioned are occurring then it's a sure indicator of diminished cooling due to low water flow rate, a partially clogged heat exchanger, or both.
 

BillyK

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Jan 24, 2010
502
Catalina 310 Ocean City, NJ
My fathers gasser had a real steam problem.. To the point where it would take the wrinkles out of anything in the cockpit.. The heat exchangers were fouled. Full of calcium deposits.
 
Apr 20, 2010
119
Hunter 34 San Mateo
The white smoke has dissipated a bit when I was under load at about 2600 RPM (3-4 knts), but I can't tell if its steam or combustion. However, I do like Ivan's explanation about having a partially clogged heat exchanger. My heat exchanger was completely clogged a few months back to the point of obstructing water, and I had to clean out a 90 degree fitting leading raw water into the mixing elbow.
 

Johnb

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Jan 22, 2008
1,286
Hunter 37-cutter Richmond CA
Are you getting plent of water coming out of the exhaust? My 3QM30 puts out about a cup per burp (very scientific I know) and that is about every 3-5 seconds at idle. When I had a raw water restriction it sounded differant and did steam. When normal there are copious quantities of liquid water and the exhaust sounds muffled due to adequate cooling of the exhaust gases.
 
Jun 4, 2004
2
- - Vancouver
mixing elbow

If you have not changed your mixing elbow in the past few years that will likely be the cause of your smoke. From my experience even if you seem to have enough water coming out of the exhaust it does not mean that your mixing elbow is not almost completely clogged.
 

Johnb

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Jan 22, 2008
1,286
Hunter 37-cutter Richmond CA
If you have not changed your mixing elbow in the past few years that will likely be the cause of your smoke. From my experience even if you seem to have enough water coming out of the exhaust it does not mean that your mixing elbow is not almost completely clogged.
Exhaust gas or water clogged or both?
 
Jun 4, 2004
2
- - Vancouver
Exhaust soot clogs up the mixing elbow. Happens quicker if you do a lot of idling or don't run the engine hard enough (low RPM) on a regular basis.
 
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