Sooty Rain

When my dry stacked engine has sat for a while and I go to start it I get black spots all over the back deck. It appears to be water and soot. The only explanation I can think of is that water is condensing in the exhaust pipe and or vertical muffler. The pipe is only 1 1/2" and I put a cap on the top when I leave.

Why it is never a good idea to tie up downwind of a dry stack boat.
A friend of mine had to deliver a bottle of scotch when the nearby boat was pristine, with a picky owner.

I have a dry stack also. I cover mine when the engine is not operating.
A lot depends upon:
--engine condition. As engines age they may put out more soot which collects in the stack to blow out at inopportune times.

--how you run the boat. If you run the boat too easily it may not get hot enough to run efficiently by not coming up to full temperature. Cool combustion chambers do not burn fuel well. Also the slower or lower flow exhaust stream will allow more soot to collect inside the stack to later blow out.
Run the engine harder periodically in gear before shutting down. NOT WOT , just somewhat more than your normal cruise rpm.
--sometimes the fuel. I have no choice in my home port so get ~15% biodiesel and it runs cleaner that I can determine. Yes, burn a bit more but I'll take it.

--overpropping. THere is something to be said for overpropping but , that I've seen on mine, that contributed to my periodic sooting. I was burning the same fuel overpropped that I was was correctly propped at the same boat speed but was turning fewer revs to do so so the intake air was reduced which resulted in dirtier burning. I immediately could see the results when the prop was depitched. It wasn't a lot but it made a big difference in the smoke.

--Coolant temp. Yes , I'm reaching a bit here but I think it goes along with combustion chamber temps if too cool. What is the thermostat rating. I would not worry to much about this untill all else is looked at

C lectric said:

I have a dry stack also. I cover mine when the engine is not operating.
A lot depends upon:
--engine condition. As engines age they may put out more soot which collects in the stack to blow out at inopportune times.

--how you run the boat. If you run the boat too easily it may not get hot enough to run efficiently by not coming up to full temperature. Cool combustion chambers do not burn fuel well. Also the slower or lower flow exhaust stream will allow more soot to collect inside the stack to later blow out.
Run the engine harder periodically in gear before shutting down. NOT WOT , just somewhat more than your normal cruise rpm.
--sometimes the fuel. I have no choice in my home port so get ~15% biodiesel and it runs cleaner that I can determine. Yes, burn a bit more but I'll take it.


--Coolant temp. Yes , I'm reaching a bit here but I think it goes along with combustion chamber temps if too cool. What is the thermostat rating. I would not worry to much about this untill all else is looked at

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I stated here before that my engine, a Yanmar 3HM, was originally designed as a raw water cooled engine (now dry stack and keel cooler) so the operating temperature is low. I have thought about it a lot and have gotten opinions and suggestions concerning raising the operating temp with different thermostats (engine has 2) or some kind of remote thermostat bypass but I haven't done anything about it. I hadn't connected the soot with lower operating temps though.

Brings back memories. My folks used to call them "tar balls"! When my dad started his tugboat business in Seattle after WWII, he had all manner of old wood tugs with various diesel engines. One in particular a Fairbanks "Remorse" as dad called it, would do that every time he fired it up and often underway. My older brother spent lots of time on the boat as a baby as they lived aboard between log tows and my mom would put him in a crib on the back deck on nice days and it made her madder than a hornet to look in the crib and see the baby covered with tar balls! Dad would get a real earful!!

I've had my boat for over 30 yrs. I went to 180oF stats from 170oF over 25 yrs ago. Didn't really make a lot of difference.

As a keel cooler cooled engine now you could raise the operating temps to 160 or 170oF and I suspect your engine will like it.

Low temps stats of approx. 140 to 150oF are normal for a raw water cooled engine to avoid plating out of salt in the engine if the operating temp is any higher.


You no longer have that concern so try the higher stats.

I don't know that a higher operating temp will help but I suspect it will. With the reminder that your engine was converted from raw water cooling to a closed system, keel cooler, then the need for the low temps is gone and maybe now is causing you trouble.

But also consider the operation.

The diesel today doesn't burn as hot as pre EPA diesel. Especially as it ages. Many of the additives refiners put in the fuel dissipate in a few months, so old fuel in your tanks will cause more soot. People with diesel stoves and heaters can have the same problem. Adding a catalyst when fueling gives more power, uses less fuel and a hotter/cleaner burn.
I use Archoil AR6200 and get 6-10% better mileage and little or no soot from my diesel stove or boiler.

koliver said:

Why it is never a good idea to tie up downwind of a dry stack boat.
A friend of mine had to deliver a bottle of scotch when the nearby boat was pristine, with a picky owner.

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What do you do when you're tied up at your home berth and a big Nordhavn 86 ties up in front of you?
After it left my dock neighbour and I had a lot of soot on our decks, and it didn't clean off easily.
But since my dock neighbour also happens to be the marina maintenance manager, transient Nordhavns are now given berths well away from us...

My mechanic said that if not properly baffled the lack of exhaust back pressure will cause more oily soot to appear out of the pipes. I don’t know