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Old 28-05-2011, 14:43   #1
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Black Exhaust Water - Soot ?

I bought a 1979 pearson 32 about three months ago with a Yanmar 2gm20f. Until last week I ran the engine at around 2200 rpm cruising. Then I realized it wants to be run higher and recommended speed is 80 percent of max. So, the last time out I cranked her and all was well. Today went out and after five minutes noticed black stream in the exhaust water (not smoke). It may have been there from go but I didn't notice. When idled down no black. When run under high rpm with no load (neutral) no black. I took a sample of the black water and it is not oil, it's sooty. Engine doesn't seem unusually hot and gas who be fine. Don't know about filters, haven't checked.

Is it possible that the two hours max i ran engine at 2000 cruising over a couple of months built up so much soot in the elbow or muffler that i just need to blow it out by running at high (correct) speed? I didn't persist since black stuff coming out the back the boat freaks one out.

Bottom is clean and i don't think there's a prop issue (it's folding) and there is no rough running, trouble starting, speed fluctuations etc..

Thanks!
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Old 28-05-2011, 14:47   #2
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Re: Black exhaust water - soot?

Diesels do need to be run at higher speeds and heavy loads to get the combustion chamber hot enough to blow out the carbon. For my diesels Cummins specifically states this and requires it as well.
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Old 28-05-2011, 15:12   #3
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Re: Black exhaust water - soot?

Quote:
Originally Posted by sandycohen View Post
Is it possible that the two hours max i ran engine at 2000 cruising over a couple of months built up so much soot in the elbow or muffler that i just need to blow it out by running at high (correct) speed? I didn't persist since black stuff coming out the back the boat freaks one out.
I am doubtful but giving the engine a really good workout ought to clear it out once and for all. Plus you don't know how the previous owner used it. Ours had been used very gently and took a 14 hour blast across the English channel in a gale to clean it out. Started much better after that.

The other point though is that it could be over fueling, perhaps an old air filter (ours is foam) or the pump not set properly and that isn't a DIY job.

So what to do about it. Check the engine air filter if it has one. Check air can easily get into the engine bay, run it with a panel out, check that the boat reaches the correct speed although you have said hull and prop clean. If okay give it a good run.

Pete
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Old 28-05-2011, 15:31   #4
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Re: Black exhaust water - soot?

We had some black non-sooty looking material come out of our boat a few times in a row, I changed out the impeller on the raw water pump and it stopped.
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Old 28-05-2011, 16:12   #5
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Re: Black exhaust water - soot?

Thanks everyone for the replies.

Jiffylube - is definitely sooty looking - I caught it in a bottle and can see it is particulate stuff

Pete7 - I don't have starting problems. If I haven't been out in a week it may take max 15 seconds to turn over usually less. if I've been there within the past day or two, starts almost immediately. Were you having black water, or just starting problems?

I don't think it has an engine air filter - there is nothing in the air silencer.

You mean run it with the engine access panel open? I can't imagine that's the issue as it has full access aft into the transom which is vented.

No need to look in the muffler?

Also what is a muffler on a boat - really just a fancy thing to keep water from running back right?
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Old 28-05-2011, 16:24   #6
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Re: Black exhaust water - soot?

You may find that the prop is a little too big for the boat, i.e the engine is struggling to push it, a bit like when you see black exhaust out of a lorry when it's going up a hill because the revs can't match the fuel input.
Assuming the engine is in good shape, injectors are clean, adequate air supply, correct running temperature etc etc.

re.the muffler, a muffler is to reduce noise, a water lock prevents backfilling, obviously some do both, but they are different.
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Old 28-05-2011, 16:31   #7
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Re: Black exhaust water - soot?

Have a read of this, it suggests the engine does have a filter:

Torresen Marine

Whether yours has one is a different question but worth a check. Black soot is a sign an engine is over fueled because it can't breath properly. There is also the chance the engine exhaust elbow which mixes the cooling water to the exhaust is blocked. That is a case of taking the hose off and having a look, indeed it could be the hose too.

It will be something simple and easy to fix.

Pete
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Old 28-05-2011, 16:37   #8
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Re: Black exhaust water - soot?

Here is a previous boat I had, which would leave a trail of soot on the water at slow speed until 1800 revs and the turbo kicked in. Once the turbo was up to pressure the air/fuel mix would be correct so the exhaust would run clean. However, under acceleration the fuel/air mix was way out so lots of soot.

Did have some interesting comments from any friend who tried to follow.

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Old 28-05-2011, 17:16   #9
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Re: Black exhaust water - soot?

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Originally Posted by Pete7 View Post
Here is a previous boat I had, which would leave a trail of soot on the water at slow speed until 1800 revs and the turbo kicked in. Once the turbo was up to pressure the air/fuel mix would be correct so the exhaust would run clean. However, under acceleration the fuel/air mix was way out so lots of soot.

Did have some interesting comments from any friend who tried to follow.

Pete
That just has to be one of those so rare diesel outboards?!
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Old 28-05-2011, 17:22   #10
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Re: Black exhaust water - soot?

Pete7 - I don't know if the boat in your picture is water cooled, but mine is (obviously) and the soot is NOT in the air - it's in the water - it leaves a trail of inky water behind the boat (not oily at all).

If I can get the same hull speed at 2500rpm or 3000rpm, and no ink with the former, is it necessary to resolve the issue so that I can run the engine at the recommended cruising speed, or should I just throttle back down and forget about it?

Is it doing damage to the boat to have the black stuff in the exhaust (unburnt diesel or soot)?
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Old 28-05-2011, 17:27   #11
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Re: Black exhaust water - soot?

It's actually a Ford Dover 4.2L, 4 cylinder block. About 80 gee gees in a truck, but with a bit of magic and a bigger turbo by Mermaid Marine puts out 200 hp.

The price you pay for the extra hp though is the engine is over fuelled on acceleration because its mechanical govenor can't cope with such a big range.

Sandy, sorry for the thread drift.

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Old 28-05-2011, 17:30   #12
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Re: Black exhaust water - soot?

PS - There may be a missing air filter, but if that's the case, is there any way that would be causing the problem?
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Old 28-05-2011, 17:31   #13
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Re: Black exhaust water - soot?

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Sandy, sorry for the thread drift.

Pete
That's OK, do you think you could comment on my last question above this though?
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Old 28-05-2011, 17:34   #14
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Injectors...

Am I going blind or has no one suggested that the injectors may need an overhaul?
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Old 28-05-2011, 17:35   #15
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Re: Black exhaust water - soot?

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Originally Posted by sandycohen View Post
Pete7 - I don't know if the boat in your picture is water cooled, but mine is (obviously) and the soot is NOT in the air - it's in the water - it leaves a trail of inky water behind the boat (not oily at all).

If I can get the same hull speed at 2500rpm or 3000rpm, and no ink with the former, is it necessary to resolve the issue so that I can run the engine at the recommended cruising speed, or should I just throttle back down and forget about it?

Is it doing damage to the boat to have the black stuff in the exhaust (unburnt diesel or soot)?
Boat in the picture is water cooled, but above waterline exhaust and no silencer, just straight though Even so left a trail as the water cooling left soot on the surface.

Running your engine at 2200 I think you said is still a good speed and its not going to glaze the bores at those revs. However, the soot is going to slowly clog up the exhaust and make a sooty mess on your hull, so if you can find the reason and it will be something simple then worth doing.

Pete
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