Black Exhaust Water - Soot ?

[JiffyLube]

I think the only way to know what this black stuff is, is to get it analyzed.

[Cheechako]

Well...reading your post...if you can make 3100 rpm max....hmmm....doesnt seem like you're too over propped.... what's max on that engine? 3600?

[sandycohen]

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.

[Capn Morgan]

Originally Posted by sandycohen

Hi All - First, thanks again for everyones input.



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.

If the water is coming less and less black now (am I right understanding this?) it means the exhaust system is being cleaned up by the high power running. I would do it a few more times until it clears up. I did it on mine and it seems to go sweet. Also, the PO is saying correctly that in a perfectly matched system you would get max power at max rated RPM and the boat would be at max hull speed. It is also true that not all boats are set up like that. If you are over pitched, you will be getting more power at less RPM, but you will also get less max power: the engine will not get to the max power setting. Again, this may not be a problem at all, except that it will start throwing black smoke. My prop is over pitched and I am not in a hurry to correct it because I would need more RPM to get my comfortable cruising speed with the associated noise increase. I just run the engine at max power to get rid of possible deposits from time to time.

I don't think you have a problem in your hands, I don't think the PO is wrong either. Just clean the exhaust, check the injectors, filters etc and you won't worry about it anymore. If the prop is bronze you could have it re-pitched as well, they do it in some places. I didn't bother with mine and it all seems to be going ok. Only trying to pass on experiences. Hope they are useful.

Hey, thanks for the update. It's really interesting reading. I keep learning every day too. Cheers!

M

[sandycohen]

Hi Capn -

I am anxiously awaiting Nigel Calders books so I can ask more intelligent questions about rpm/power developed/horsepower etc.. but here is the question I can't get my brain around:

If an over-pitched prop means that you get to the same hull speed at a lower engine speed then you would with a correctly pitch propped, which translates to less fuel and noise, why is the over-pitched prop not the perfect pitch? Is there less acceleration because at the lower rpm you can't develop speed as quickly and that is the trade off?

OK - Also on the injectors, forgot to add - I have separate decompression handles for each cylinder. I threw one at a time and the engine started sounding terrible. Is any further check necessary?

[Cheechako]

"If an over-pitched prop means that you get to the same hull speed at a lower engine speed then you would with a correctly pitch propped, which translates to less fuel and noise, why is the over-pitched prop not the perfect pitch?"
It has to do with the Horsepower/torque curve. Each engine has an optimum point at which it is most efficient, durable etc. I think you previously said you can get to 3100 rpm...? If so you should forget about the overpitched thing. Also, I keep reading about maxing the rpm in neutral, Never do that! Not good with an unloaded diesel... and some of the Yanmars are prone to cracking the piston skirts...

[Capn Morgan]

Hi Sandy

Cheechako basically answers it. The thing is, if you make all the calculations for a boat, it may be that you need a 47 hp engine. If none of the manufacturers of the time make such an engine, the boat builder will have to choose from, say 40 or 55. The logical thing is to choose the 55, but that means you have more power than you can use so you attempt to pitch the prop so that you get your 47. As all calculations can have an error (many are empirical), it may be that you get it a little overpitched which means you will never get the full power or RPM of the engine, but you will still get enough power to bring you to the max speed. It is not the ideal situation, but you can live with it.

I would not be able to answer your question on the decompressors. Sorry. Also, Cheechako points to not taking the engine to max RPM with the engine unloaded. He has a point, it is only something you do for testing purposes and for a very short period of time. Agree entirely. You've already done it so you don't need to do it again. It works.

Cheers!

[Capn Morgan]

Hi Sandy

Have you solved the problem? Any idea what it was in the end?

Cheers

[sandycohen]

Capn Morgan et al -

thanks for the follow up. First and most importantly I've been sailing the boat alot without issue since all of this. The problem is basically unchanged (inky water).

Reading back through the thread, it's shameful that I took so much of everyone's time when I didn't even know the condition of the fuel filters.

I did change both filters, and when I saw them, was very optimistic that I'd found my issue. I have two primary fuel filters (filters that are between the fuel tank and the engine). They are different models - one is spin-on and one is replaceable, both have sight bowls for water. When I removed the filter closest to the tank, it was black and gunky, really unimaginable. The next primary fuel filter was pretty much clean, and the secondary filter (the one mounted on the engine) also was without any visual soiling.

So, I replaced the two primaries with the spares that came on the boat, and put the secondary back in as I didn't have a spare and it looked fine.

After hours figuring out how to bleed the fuel system and probably screwing up other things, I got the motor running and was looking forward to the disappearance of inky black water with my new clean filters. Negative - same problem. Basically at that point I decided to stop considering this a problem and just assume the prop was pitched such that I needed to cruise below yanmars recommendations.

Next thing that happens is I get online to order my replacement filters so I have spares, and I realize that the first primary filter (closest to the tank) original and spare I since replaced it with were 2 micron filters!!

So that explained why it was so unbelievably filthy and the others were so squeaky clean. The question is, and I haven't answered it yet, does that restriction also give us an answer for the inky black water? I would think that a fuel restriction would result in not enough fuel, as opposed to excess fuel not being burned. But who knows?

I haven't gone back to change the 2 micron filter out yet because I am lazy and it makes such a god awful mess. The next primary filter is 20 micron, and then the final yanmar OEM which i think is 2 or 5 or something.

Thoughts?

S

[captain465]

Very unlikely that the filters are a problem (filters should get finer and finer as it travels toward the engine)
More likely is that the engine was not run for a long time, and the renewed flow of cooling water through the exhaust system is loosening carbon that was built up and is now dried out and eaiser to dislodge. It should start to "clear up" as it is used.

[boasun]

Replace your air filter... Had a smoking diesel and it was due to its being starved for air...

[sandycohen]

Air filters fine. Not having smoke problems.

[saben]

Try having the injectors serviced. If giving of a thick, concentrated spray pattern from the tip of the nozzles instead of a fine mist its going to do black smoke, soot, what ever you want to call it. 800 hour between injector servicing is what marineized Kubota diesels recommend. This would be my first plan of action. Good Luck.

[Capn Morgan]

Hi Sandy

I do no know enough to talk about the external filter sizes. Mine are 2 micron because I want them to stop anything before it gets to the engine mounted filter. The Racor ones are much cheaper and easier to replace than the Yanmar ones.

As for the soot, I agree with the post above in that I think it is old carbon deposits in your exhaust system that will either clear up in time with use or you are going to open it and do it yourself.

Either way, good to read your follow up, keep sharing the fun!

Cheers

M

[bstreep]

I didn't see anything about your mixing (exhaust) elbow. Has this been checked? I just cleaned both of ours in the last month (engine & generator).