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Ink black exhaust water - soot?

15K views 46 replies 16 participants last post by  gamayun 
#1 ·
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!
 
#3 ·
bub is right,the black soot is caused by overloading the engine,yanmars are famous for this,what makes you think it needs to run at a higher rpm?throw the tach away and use your better judgement,higher rpm's should only be used in an emergency situation and only for a very short peroid
 
#4 ·
1. Per the original post, is it possible I am just blowing out carbon buildup in the system from my low rpm runs? Is it dangerous to the engine to run with the black exhaust water to test the theory?

2. Everywhere I look online says Yanmars DO want to be run at 80% of max output which would be 2720 - are you saying that is wrong??

3. The PO installed the folding prop and didn't have this problem.
 
#6 ·
Bubb - Is there anything damaging to the engine about having black ink in the water, other than to the environment?

Am I correct that it is necessary to correct the pitch, rather then just idle down and achieve the same speed, because then i am running too low an engine speed which will cause soot and black smoke?

The stuff in the water is black particulate - is that what unburnt diesel looks like?

Guess I better read up on what pitch is and how I adjust it!
 
#7 ·
It is a good idea to run the engine 75 - 80% of max. Diesel engines like / want to be run.This is what Mack Boring will tell you if you take one of there maintenance classes. In fact the guy teaching the class suggested going out once a season for a couple of hours and running the boat like a powerboat. The issue for us sailors is that a lot of time the engine never gets a chance to run at operating temps long enough to stay 'clean'. I know that my engine only runs for about 20 minuets when I go out and when I come back.
 
#8 · (Edited)
Dive on the prop, it could be barnacle growth. But if the prop is clean then I would play with the pitch. I am not going out on a limb and tell you that this could not be damaging. What I do know is if it is not taken care of it will get worse. BTW, when I am motoring I am at half throttle or about 2200 rpm. That seems to be the sweet spot for my boat where the engine is the smoothest and I get the best fuel consumption 1/4 gal an hour. The difference in speed is 5.4 knots compared to 6.2 knots at 3/4 throttle and using 1/2 gal of fuel an hour.
 
#9 ·
Bubb - You have a 2gm20 as well?

I have an off topic question that another owner could answer - the oil dipstick (on the engine, not the tranny) has a huge distance between the high and low marks - like almost the entire blade of the dipstick - is yours that way too? It seems hard to believe that the high and low acceptable range could be so far apart unless the resevoir comes to a very narrow point where the dipstick goes, or it curves in a crazy way.

thanks!
 
#14 ·
your 2gm has only about a 2 quart capacity,if your having problems keeping at the full level you have bigger problems and to your other question,its a small engine pushing a heavy boat any extra load will cause an overload,over proped,dirty bottem or even a extra large alternator when its fully charging,i run my ysb 12 at about 1/2 throttle [no black smoke]and don't get much more significent speed at more,btw your tach may be wrong
 
#15 ·
Bubb - Sorry if I have gotten your bad side, not sure why you don't want to agree on anything that you seem to agree to.

For everyone else - an update:

Went out for a sail today.

First,- 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, as sawingknots pointed out wisely, 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.

Thanks to all.
 
#46 ·
A quick search showed the max RPM of your engine to be 3600, and you are only able to get 3100. So why don't you start with the prop?

Bubb - Sorry if I have gotten your bad side, not sure why you don't want to agree on anything that you seem to agree to.

For everyone else - an update:

Went out for a sail today.

First,- 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, as sawingknots pointed out wisely, 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.

Thanks to all.
 
#17 · (Edited)
You haven't got on my bad side. I am just a cranky old man that has been around boats for more than 50 years. The reason the exhaust gets darker as the engine speed increases is as you are increasing the throttle the more unburnt fuel you are putting though the engine. Do you know when that prop was put on the boat? Did you do a sea trail when you bought the boat? If you did have a sea trial was the engine ran at full throttle for 5 to 10 Min's. When you bought the boat did you have oil analysis done to check for particulates and contaminates in the engine oil including unburnt diesel?
 
#18 ·
You are close to your hull speed at 6.5 knots - hull speed being 6.7 knots for your waterline of 25'.

The correct prop will let you achieve max rpm and ideally no more. If the revs exceed max rpm under power you are under propped. If you cannot hit max rpm you are over propped.

I would check the exhaust elbow in any case. If it hasn't been checked in recent years it could be restricted by carbon. They regularly corrode from the inside as well.

When an engine works too hard it will exhaust unburned fuel.

An accurate tach would help.
 
#19 ·
i have a 2GM20F. most of the time i run at 2250. this does not hurt the engine, & saves fuel . wide open it will get up to 3600 and 6.9 kn which is hull speed. no soot. if your engine will not go to max rpm your prop has too much pitch.
 
#20 ·
copied from another forum

Black Smoke and Exhaust Problems
I am hauling our boat soon and I was wondering about our prop and if it is the correct size for the engine. I say this since the engine will start to blow black smoke once it reaches 2900-3000 RPM. Dave

[JED] This must be corrected, as you are limiting the useful working life of the engine. Possible reasons for black smoke -
  • prop pitch is excessive [engine is overloaded and is running too rich]
  • dirty bottom or prop
  • transmission problem
  • old fuel [very common]
  • kerosene being burned instead of diesel fuel
  • air inlet restriction
  • turbo problem [only for turbo charged engines]
  • engine cannot get enough air while running at high rpm [engine space not properly ventilated]
  • restricted intake or exhaust valves
  • improperly adjusted valves
  • restricted exhaust system
  • injection timing incorrect
  • injector problem
  • low engine compression
  • engine is not reaching correct operating temperature
I would check the simple things first, as in the list above. Did your boat always have this problem, or did it develop suddenly, or gradually?

If your fuel supply [in the boat] is more than 6 months old, and no fuel stabilizer has been added since you filled the tank, it is suspect. Most sailboat fuel tanks contain at least SOME very old [several years] fuel. The tank should be pumped dry, inspected for condition, and fresh fuel [with stabilizer] added. Also change all fuel filters.
 
#25 ·
Hi All - First, thanks again for everyones input.

Two things to add to the thread.

First, I opened the boat to full throttle in idle to see what max RPM I could get to. The answer is about 3400 and the throttle control is hitting the transmission lever which in neutral is right behind the throttle control which in the real world wouldn't be a problem since it isn't necessary to go wide open in neutral. While trying to inch the transmission control down to find the end of the throttle travel, i accidentally (although I guess I should've seen it coming!) dropped the tranny into reverse at about 3500rpm - probably did more damage then the rest of this issue ever will (seriously, does anyone think that one time shift is something i need to worry about or do anything to check damage - I shifted in idle several times fwd and rev after and all seemed fine).

So, it appears in idle the engine can hit max rpm's or something every close to it.

I did get inky water in idle running high rpms the first time I opened it up wide. The 2nd time I did it againt o try and find the rpm where it starts and it didn't turn inky, but i would say the water still had a grey tint and there was greyish exhaust smoke.

To point out something else I've never said before, I normally get NO exhaust smoke, and even when i have inky water there isn't always any visible exhaust color.

The next thing I want to report is that the PO responded to an email from me asking him if he'd ever seen inky exhaust water, what his cruising rpm targets were, and if he purposefully overpitched the prop - response is below in a couple of threads:

From PO in reply to a voicemail I left him:

Anyway, black exhaust is usually caused by unburned fuel, in turn caused by engine overloading - for instance, the throttle is pushed all the way up calling for more engine speed, but the engine just can't get there because of big waves, heavy load, or the displacement hull just won't go any faster.
I think you mentioned something about max rated engine RPM. You are only going to get there if the prop is perfectly pitched for the particular boat and engine combo, which can be hard to achieve in the real world.
So, in reality, if you see black exhaust water throttle back just a little and it should go away. If you want to pull the exhaust elbow it can't hurt anything, but it might turn out to be a PITA job. Hope this helps.

My reply:

Basically since I had the boat I had been cruising around 2200rpm - I think maybe this is what you told me was your guidelines. Then I read things online that says the engine wants to be run at 80% of the rated continous rpm, which would mean a cruising rpm of something like 2800-3000. When I started doing that I got the inky black exhaust.

I've posted the issue on two message boards and gotten a lot of great advise. I didn't think the issue could be pitch (what people call being overpropped I guess) since you had bought the prop special I figured you got the appropriate size one. Some people did say that some owners intentionally overprop the boat to reduce noise and fuel consumption by running lower rpm's - did you do that on purpose?

His reply:

Yeah, the boat might be a little overpropped, but not on purpose. I installed the prop the dealer recommended, and it wasn't worth it to me to haul the boat back out, send the prop back, and install another one to get the pitch just perfect. I think 2400 RPM or so would be a good long-distance cruising speed and 2600-2700 if you were in a hurry and not too concerned about fuel consumption. It's not so much percent of rated RPM that you are looking for, as much as percent of rated power output. If the prop is perfectly pitched, the two go hand in hand, but if the pitch is a little high then you get higher power output at a lower RPM
.

I bought the boat largely based on my experiences with the PO and knowing that he is both more knowledgable on all systems than I am, and more careful/concientious I suspect than I am on taking care of things. So I am going to basically now use his RPM guidelines, maybe check the elbow when I get a chance, and forget about it! But, since everyone got behind me to try and figure this out, I wanted to give you more info, and if you want to keep discussing or have other thoughts, please share.

Disclosure, the PO is now probably reading this thread so be diplomatic.
 
#27 ·
Decompression levers are for starting, either by hand or to help spin it before electric starting. I've always heard that releasing the compression on a running engine is a good way to do some serious damage to the valves and wouldn't recommend it.
 
#28 ·
Uhoh - I hope what you've heard is one of those hyperbolic tales that is a warning of something that could but usually doesn't happen.

Can anyone else chime in on whether flipping the levers very briefly at idle speed in neutral may have damaged the engine, and what I can check to see if it did indeed?

Sandy
 
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