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  Topic Review (Newest First)
02-12-2013 05:35 PM
Re: Oil in exhaust?

Have you always seen grey smoke at lower revs? If you haven't, check to make sure everything else is normal like engine operating temperature.

Have you always seen black smoke at the higher revs? A little bit of black smoke at high loads is perfectly normal on older diesel engines. They allowed them to overfuel a bit to get the horsepower rating up, the newer ones don't do this because of emissions. The only real downsides to it are it is worse for the environment, your mileage will be worse, and you can damage pistons and valves in extreme cases with high exhaust gas temperatures. If the black smoke is new and everything else being normal such as the boat speed versus the rpm, the first thing that I would look at is the air filter, a plugged filter will cause this.
02-11-2013 11:59 PM
Re: Oil in exhaust?

Did you see oil on the water? If not, then you probably aren't exhausting oil.

Other than that, black smoke can mean barnicles on the prop. (At haul, out, I had 6 feet of line wrapped around the prop.)

I suggest you buy a mask, fins and a snorkle (and wetsuit). Like owning a Mast Climber, it pays for itself quickly.

02-11-2013 07:21 AM
Re: Oil in exhaust?

Your diesel could use a decarbonization via the fuel tank and the crankcase oil. Improvements will be noticable quit soon after using "Seafoam", obtainable from any automotive store.
02-11-2013 05:36 AM
Re: Oil in exhaust?

oil in exhaust is generally from the oil cooler. Sea water cools the oil and because oil pressure is more than water pressure, oil passes to the cooling water and finally to exhaust.
02-11-2013 12:37 AM
Re: Oil in exhaust?

Great explanation! On a 2 day cruise we just got back from, I saw both smoke symptoms. Black when I tried higher revs and thin grey smoke at low revs. I'll look into cleaning something and get some help. The boat speed was fine & as anticipated at whatever RPM I tried, so any mud on the prop is long gone.
02-09-2013 08:49 AM
Re: Oil in exhaust?

In a boat, it is important to understand that the load on your engine is tied to your rpm and speed through the water. The load on the propeller determines the load on the engine and the engine will happily run at any rpm unless the load is greater than the power that it produces at that rpm (this is the problem with being overpropped). If the boat feels slower at a given rpm, it is not an indicator of the engine being down on power, it is an indicator of more drag or a less efficient propeller. In your case, it sounds like you were aground so that may well have put more load on the engine. It may well be that you were getting close to the edge of your available power for the given rpm so the engine was fueling heavily which can lead to black smoke.

Gray smoke indicates poor combustion in the cylinders. Common causes are incorrect injectors (this is only a problem for the guys building performance diesels) and a cold engine. From your post, it sounds quite plausible that your engine was cold so that may be the explanation. Black smoke is from overfueling and you don't have enough air to fully burn the fuel. This occurs when you really load down the engine. On older naturally aspirated diesels, this is controlled through a fuel plate normally which controls how much fuel is available at any rpm, on turbocharged ones there is an air fuel control which supplements the fuel plate to control fuel based on turbo boost. If you have a common rail engine, then it is likely that you have a MAF sensor that controls this. This is all a bit off the subject but it controls your smoke producing ability to meet emissions regulations and keep your engine together.

If your boat goes back to motoring at normal speed for a given rpm and you don't get anymore smoke, I wouldn't worry about it. If you motor too slowly, then you should check the prop. If you motor normally and get smoke, then look at the color and try to determine when you get it and someone should be able to help you.
02-09-2013 12:18 AM
Re: Oil in exhaust?

Thanks to all!
We weren't grounded hard. My son noticed the helm was not responding, and there we were. We sailed into it, then after the rising tide & jib pulled us out to a slow sail, then I turned the engine on. So, I'm guessing there is some 'stuff' on the prop, which would have been folded when we grounded and then pivoted in the mud as the freeboard caught the wind after we took the sails down. I'll try 4 hours of motor/sailing this weekend, and if still an issue I'll have to pay the diver.
02-08-2013 12:15 PM
Re: Oil in exhaust?

Originally Posted by jrd22 View Post
If the engine revs up normally in neutral, but continues to smoke when in gear you should check the prop. You might have something fouled on it, a piece of line, etc.
There's been plenty of it around too. A big ebb stirs it all up, lot's of crap in the water around low tide.
02-08-2013 11:38 AM
Re: Oil in exhaust?

If the engine revs up normally in neutral, but continues to smoke when in gear you should check the prop. You might have something fouled on it, a piece of line, etc.
02-08-2013 11:08 AM
Re: Oil in exhaust?

Trust the dipstick.

Overfilling with oil will produce black smoke.

Like said chances are 1 you have fouling of the prop/shaft which will slow you down and make you produce black smoke when run hard, If you were grounded hard and if you ran the engine a lot and sucked up lts of mud its possible you sucked some into the engine, but it should clear.

Look for the simplest first....fouled prop
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