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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 07-14-2008
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Black smoke and black water

Had to motor more than usual this weekend against a hefty wind. When I brought my 2QM15 up to 2600 -2800 rpm the exhaust turned black and the water being expelled out the back was also black. I usually cruise at around 22-2500 and have had few problems. I do confess that the oil level is slightly high. Not a pint or anything but slightly above the full mark.
Also after stopping the engine and sailing in choppy water, gusty conditions then restarting the engine the exhaust water wasn't sufficient enough to cool the engine. I had to shut her back down and sail some more. I opened up the raw water strainer to see if I had a problem there. None, but when I restarted the engine a few minutes later the flow was once again good. Did opening the raw water strainer break an air lock or did I just luck out? Any advice would be appreciated.
Thanks,
BruceyP
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Old 07-14-2008
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Check your exhaust Muffler

You probably have excessive soot buildup which is a) causing the black water/smoke and restricted flow out the back.

DrB
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Old 07-14-2008
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Bruce,
Had the identical problem with my 1GM10. The mechanic said that the load exceeded the design parameters and that incomplete combustion occurred causing the smoke and black water. He suggested getting the injector serviced and to polish the fuel. I also added a little cetane and adjusted the valve clearance to spec and can rev up better now but can still stress the engine at above 3300rpm. The water flow was probably a short term thing as it takes a few seconds for the flow to exit the muffler. That's my guess, as long as the overheating signal didn't go off.
Doug
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Under heavy load, my motor will do that. It has been prone to it for at least 15 years. It is unburned fuel. New injector noses improved it about 10 years ago, but it still happens if I really load the motor. You see it often when the motor is loaded at the dockside and the soot builds up on the water.

Last edited by Rockter; 07-14-2008 at 04:24 PM.
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Old 07-14-2008
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Mine coughs one puff of black smoke and about a pint of black water at start-up without fail. Then it's smoke-less with clear water. I've always assumed it was the extra fuel in the chamber that was shot in there during the 3 seconds of cranking before ignition.
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Black smoke is caused by too much fuel and / or not enough air entering the combustion chamber. Causes can be...

- a blocked air intake
- lack of airflow into the engine room (did you add extra sound insulation?)
- engine room temp too high (causing hot thin air entering the motor) it should be under 130F in there
- excessive load on the engine, such as...
- dirty bottom & prop (especially when combined with a headwind and chop)
- rope caught in the prop (you probably would have noticed strange thumping or vibration)
- forgetting to weigh anchor

The overheating was probably caused by the engine overload. It also points to a possible

- clogged sea strainer
- partially broken impeller in the sea water pump
- heat exchanger core that needs to be removed and cleaned

Also, a exhaust elbow that is partially clogged with carbon could cause both the engine overload (from back pressure) and restrict the seawater flow.

You should work though these, eliminate them as you go until you find the problem. It could be a combination of a few of them. There could be other causes, but these are likely suspects. (Except the anchor thing. )

Last edited by SteveInMD; 07-14-2008 at 05:34 PM.
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I had to stop my boat this weekend, drop anchor, and dive under to chisel off the barnacles from my prop.

It's the right time of the summer for it. Same thing happened last year at this time.

The barnacles will seriously load an engine. And you end up throwing water out the sides of the prop instead of out the back.
gh

ps. use gloves! Get a mask, and I used an 18 inch prybar as my chisel. Tied it with rope to the boat so it wouldn't get lost.
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Old 07-14-2008
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A paint scraper or putty knife would probably work better to get rid of barnacles.
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A sea water air lock did not cause your engine overload and black smoke. Overheating may have been a symptom of the overload. The overheating could have been caused by an airlock or points to a weak cooling system.

Last edited by SteveInMD; 07-14-2008 at 06:18 PM.
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The thing I liked about the prybar, is that your hand is further from the barnacles on the work surface. Less chance of getting bitten.
Haven't yet tried paint scraper.
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