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Old 28-05-2011, 17:38   #16
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Re: Injectors...

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Am I going blind or has no one suggested that the injectors may need an overhaul?
Yes quite right too, just trying to remove the obvious simple items first, air in and exhaust out. Checking an air filter or exhaust is DIY and sounds like Sandy could do that himself. Pulling injectors fine but needs a high pressure spray rig to examine them for the spray pattern.

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Old 28-05-2011, 17:41   #17
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Re: Black exhaust water - soot?

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. 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.

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Pete - there is no soot at lower speeds - this problem only started when I tried cruising a the recommended speeds.
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Old 28-05-2011, 17:42   #18
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Re: Black exhaust water - soot?

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PS - There may be a missing air filter, but if that's the case, is there any way that would be causing the problem?
Unlikely. Indeed if it had one, you could take it off and see what the difference is. Less soot after a while and the filter would be blocked. If its not missing but has the wrong one in then that could cause the restriction in the engine breathing.

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Old 28-05-2011, 17:44   #19
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Re: Black exhaust water - soot?

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Pete - there is no soot at lower speeds - this problem only started when I tried cruising a the recommended speeds.
Can you remember how fast you were going at 2200 revs and what was the top speed at 3000 revs?

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Old 28-05-2011, 17:49   #20
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Re: Black exhaust water - soot?

I'm going to find out tomorrow! Sounds like if I can cruise at hull speed in flat water with an engine speed that is less than the optimal cruise speed, I may not need to be worry any further.

I just looked and adjusting the pitch involves buying new blades from denmark for my flex-o-fold prop. not interested!
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Old 28-05-2011, 18:03   #21
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Re: Black exhaust water - soot?

have you got a clean prop & hull? Increasing RPM is also increasing load & if it is loaded it will overfuel.
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Old 28-05-2011, 18:14   #22
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Re: Black exhaust water - soot?

Sandy, it sounds like you are getting rid of accumulated deposits in the wet exhaust system. If there is a way for you to open it and investigate, there should only be a very thin oily deposit inside the surfaces. See if you can clean the exhaust system before touching the injectors.

If you don't know how old the impeller is, just change it. Not worth keeping it for long and having it breaking up in the heat exchanger.

If the prop was over-pitched you would see black smoke at full power, but you would not be getting maximum rated RPM. For what you say in previous posts this is not the case.

I had the same thing happening to my genset. I took the exhaust out and cleaned it and got rid of a lot of soot that had built up over the years.

Also, run the engine hard for a while from time to time. These diesels don't thank you for treating them kindly.
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Old 28-05-2011, 18:18   #23
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Re: Black exhaust water - soot?

Nice prop If it can cruise at say 5 knots under power without soot after a run then I would leave well alone because you are gaining say 1/2 - 3/4 knot under sail over a fixed 2 blade prop.

We have similar sized yachts and I would love a folding prop but it's over $1000 in the UK.

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Old 29-05-2011, 01:22   #24
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Re: Black exhaust water - soot?

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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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Am I going blind or has no one suggested that the injectors may need an overhaul?
Ahem, cough, cough.
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Old 29-05-2011, 15:55   #25
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Re: Black Exhaust Water - Soot ?

OK - Update for Pete7 and others who may want to chime in!

Went out for a sail today.

First, I was wrong about the air filter - there is a foam air filter, and removing it had no impact on anything.

Second, prop is clear and unfouled, as is the bottom - I dove and checked - beautiful day to swim in Lake Pontchartrain.

The black exhaust water (I am going to stop calling it soot) starts to appear around 2300rpm, and gets progressively more black and less clear water as I go to 3100rpm. 2300rpm is about half throttle (based on the pedestal throttle control range, not the actual throttle arm on the engine, i didn't adjust or check that). I can get to 3100rpm at say 3/4 throttle and from there on engine speed will not go any higher nor does the engine sound any louder. Also, make speed seems to be about 2700rpm - additional engine speed doesn't make us go faster in the water that I can detect.

At 2200rpm I can move the boat around 5.5knots into a 10 knot headwind. That seems like an acceptable speed given the headwind.

Inside the sheltered harbor, I could only get to maybe 6.5 knots top with full engine speed - which is less than hull speed - more engine speed didn't make any difference.

Also I want to clarify that the stuff i am calling soot which is inky black water of varying concentrations in the exhaust, is suspended flaky particulate in the water (I took a sample) it isn't fine particles or liquid.

Also, even when I am at 2200 and the exhaust water is clear, if I take a sample of it there is some suspended particulate.

The amount of force ejecting the exhaust water doesn't seem to change tremendously as the color gets more and more black. This makes me think it isn't "cleaning" residue from the exhaust system, or it would always be the same. But my mechanical understanding of the exhaust system is nearly 0 so maybe I am wrong.

To where we left things yesterday, I am certainly happy with 5.5 knots cruising in a light headwind, as long as running at 2200rpm isn't doing me damage.

And, the biggest thing perhaps, and something that hasn't been thrown into the mix here to for I can remember on this thread, is that my tach could be wrong! But, my idle shows about 800 to 900 which seems right. And, would this explain having 1/4 of my throttle travel show no change in engine speed?

I welcome everyones comments. I did not open the elbow yet, and I certainly can, but wanted to share this info first.

Also Captain Morgan thanks for the separate post about the book - I will order it today!!

Sandy
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Old 29-05-2011, 16:20   #26
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Re: Black Exhaust Water - Soot ?

Last year my perkins had a failed injector. At cruise speed I really didnt know the one cylinder wasnt firing properly, and started up in about 2 seconds all t he time. It left black residue in the water....but surprisingly not alot of unburned fuel. Eventually I was getting fuel in the oil! that's how I found the problem. Check your oil level...is it gaining? I was lucky I found it before it destroyed the cylinder wall/rings....
If you're making 5.5 knots into a headwind at 2000 rpm in a 32 foot boat.... I would say you are way over propped....
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Old 29-05-2011, 16:52   #27
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Re: Black Exhaust Water - Soot ?

2200RPM, but yes.

Should I run it at 2400 or 2500rpm, where it's just a little black, to give the engine more speed?

As previously posted adjusting the pitch is going to cost big bucks since I have a folding prop, and I hardly use the engine - I am not necessarily looking for perfect, as long as I am not making things worse by running it in a way that works for now.

How would I know if there is fuel in the oil? Looks OK to me, level hasn't changed.
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Old 29-05-2011, 17:00   #28
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Re: Black Exhaust Water - Soot ?

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If you're making 5.5 knots into a headwind at 2000 rpm in a 32 foot boat.... I would say you are way over propped....
and there is the problem. New blades to change the pitch on a flex-o-fold are going to cost a fortune. The only other option I can think of is change the gearbox ratio, but that is likely to cost the same unless a second hand gearbox comes up.

Sandy, comparing two boats speed isn't very scientific but for comparison we have a similar sized boat (length and weight) with a volvo 28hp. At 2000 we are doing just under 5knots and need 2200 revs to make 5.5 knots our normal cruising speed. 6.5 knots is about 2600 revs and we can't make the full 3000 revs in gear.

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Old 29-05-2011, 17:05   #29
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Re: Black Exhaust Water - Soot ?

If you are not going up on the dipstick ...you're probably OK there. Frankly I would worry less about the engine rpm being high than overloading it creating unburned fuel and black soot. If it motors fine at 2200 and you dont want to repitch...just run it there I guess. The whole engine rating scheme by the industry is really wierd any way... Long story...but if you go to a commercial boat exposition. You will find the same (large!) engine model rated for pleasure use at highest horspower and rpm, intermittant duty at lower HP and RPM, and continuous duty (fishing boats etc) at lower HP yet and lower max rpm!!! SAME Engine...it's just a warranty thing...and they seem to be saying lower RPM lasts longer....never really understood the whole thing.
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Old 29-05-2011, 19:46   #30
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Re: Black Exhaust Water - Soot ?

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OK - Update for Pete7 and others who may want to chime in!


The black exhaust water (I am going to stop calling it soot) starts to appear around 2300rpm, and gets progressively more black and less clear water as I go to 3100rpm. 2300rpm is about half throttle (based on the pedestal throttle control range, not the actual throttle arm on the engine, i didn't adjust or check that). I can get to 3100rpm at say 3/4 throttle and from there on engine speed will not go any higher nor does the engine sound any louder. Also, make speed seems to be about 2700rpm - additional engine speed doesn't make us go faster in the water that I can detect.

Sandy
Thanks for the update. I'd rather be on my boat, but since I'm not, this lets me get my fingers dirty, so to speak.

IF it is carbon build up, it will be braking away from the walls of the exhaust in chunks. As you increase the RPM the exhaust gas and water rise in temperature and helps this process. The stuff mixes up inside the system and the water gets black. The back pressure from the exhaust would preclude the engine reaching full rated RPM in some cases. Again, IF this is the problem, once you have cleared it you may still find the prop to be over-pitched. Some people do this to cruise at a lower RPM for noise and fuel economy. Check if the tacho reaches full RPM without load. The governor should only allow the engine to get there and no more. This would also show if the tacho is giving you the right information, at least at that power setting.

I don't think you would be doing any damage by powering up to full from time to time. Just check the coolant temp doesn't go through the ceiling. Where I am, the waters are very warm and if I put the engine at max rpm for a while, it goes above safe limits so I have to retard it. However, this seems to be enough to keep the exhaust system clean.
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