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DrB 09-04-2007 04:45 PM

Smoke on the Water - Yanmar Question
We have a Yanmar 3 Cyclinder Diesel in our Sailboat. Can't recall the exact model, but it is FWC.

Normally we just use it to get in and out of the harbor, about 20 minutes for each run. I let the engine warm up (idle) for about 5 minutes before taking off from the mooring and a few minutes before putting it in gear to return home. We normally run it around 1800 to 2000 rpm on the motor out and in. When we return and latch on to the mooring, we let it idle for a few minutes to cool the motor down before shutting her down.

This weekend, the winds were strong and were blowing boats in all directions on the mooring field. Normally, my wife parks the boat right on top of the mooring with no problem on the first shot while I fetch the PU Buoy. This week we missed the PU Buoy for the first time by a few feet because just as I went for the buoy, a strong gust blew the bow away from the mooring just outside of my reach.

To regain steerage, she put a decent amount of throttle to start the circle turn to bring us back. As soon as she put a lot of throttle to it, lot's of white smoke came out of the exhaust. I have never seen this much before, but then again we've never missed the mooring and needed to almost fully gun it to regain control. Like I said, we don't run the engine for long, so maybe it was just some built up junk.

Once on the mooring, I put it in neutral again and ramped up the engine to see if smoke continued, but nothing. I hoping it was just blowing out some soot. At least it wasn't blue smoke.

Bottom line, should I be concerned? Plenty of clean oil, fuel is clean, and engine doesn't overheat, belts look good, only 500 h on motor.


sailingdog 09-04-2007 05:04 PM


I'd be concerned... white smoke usually isn't smoke but antifreeze or engine coolant.. that's bad. Generally, smoke from a diesel engine with problems is going to be blue or black...not white. Soot would have been black, like you see from the diesel buses in the city...

speciald 09-04-2007 05:06 PM

It is common to get black smoke when the trotle is pushed as partialy unburnt diesel ends up in the exhaust. Gray/white smoke is frequent when the engine is cold. But white smoke usually indicates water in the exhaust.

sailingdog 09-04-2007 05:12 PM

BTW, if you don't run the engine for long, that's a really good way to shorten the life of the engine.

You really need to run it under a decent load for a good period of time—at least an hour—probably every week or so... If you don't do that, the engine doesn't get a chance to burn off the carbon and varnish that forms during the combustion process and the engine never gets a chance to drive off the moisture that is present in the cylinders from the combustion process.

Letting it heat up and run at a decent operating temperature once a week or so will help prolong its life IMHO. Running an engine for only short periods of time is as bad or worse than not running it at all.

NOLAsailing 09-04-2007 05:13 PM

White smoke is probably caused by unburnt fuel in the situation you're describing. It could be coolant, but my gut tells me it's not.

Next time you're out, try motoring for a little longer and at higher RPM's to see if you can duplicate the problem. It could be as simple as an issue with the injectors. There are more serious problems that can cause white smoke, but the serious problems usually lead to persistent smoke.

I would bet the motor just had a minor hiccup when the throttle poured on - maybe a timing issue? - and some unburnt fuel appeared as white smoke.

NOLAsailing 09-04-2007 05:15 PM


Letting it heat up and run at a decent operating temperature once a week or so will help prolong its life IMHO. Running an engine for only short periods of time is as bad or worse than not running it at all.
Also, the ideal RPM will be at about 80% of the max RPM. 1800 - 2000 is probably under revving for a 3 cyl. Yanmar. You'll want to check the max RPM for your motor, but I would guess 2400 - 2500 would be about your target cruising RPM.

DrB 09-04-2007 05:30 PM

I'll keep an eye on it the next time I go out. Follow-up. The white smoke, maybe slightly grey, if it is water/antifreeze, why didn't I see on the way out, the way in, or after I gunned it again in neutral? That is the first time I have ever seen it. I am hoping it is just moisture from a cool engine that isn't run a lot.

Will do on the longer run times. Next week I'll run it for at least 40 minutes run and a decent throttle on the way out. I am also at a half of tank of diesel, so I'll need to refill this weekend with clean fuel.

Just as aside. The engine starts immediately when I key/push the start button.


Cruisingdad 09-04-2007 06:31 PM


I am trying not to regurgitate too much of what was said previously... but my guess is that there is not a problem. You are nowere near a life on that engine unless it has been badly abused. I agree with the poster above that said you are not cruising it high enough. RPM should likely be higher. In reality, most cruisers do not run their engine at those rpms because of the vibration and fuel efficiency, but check with Yanmar - they will likely tell you that it needs to be run at higher RPM's, at least periodically. That is what I do. I hate running that clap-trap at high rpms. I am comfortable with about 22-2400 on my 4jh4e, but that really is not the right rpms. So, every once in a while I get the engine up to WOT for a minute or two to blow it out, then come back down.

The smoke is not all that unusual if you do not WOT on occasion, or run it at lower RPM's for extended periods. You can always do a compression test if you feel it is necessary. But if the cooling and oil look good (and the diesel, VERY IMPORTANT AS YOU MAY BE BURNING JUNK OFF IN YOUR DIESEL), you are probably fine.

- CD

PS Just blame the wife for missing the mark (HAHA, just kidding).

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