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Old 11-06-2015, 09:13 PM   #21
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Check your engines troubleshooting section for engine smoking - black smoke.
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Old 11-06-2015, 09:26 PM   #22
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Cat 3126 engines had a soot problem and it took cat a few years to fix the problem. What engines do you have?
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Old 11-08-2015, 01:30 AM   #23
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Cat 3126 engines had a soot problem and it took cat a few years to fix the problem. What engines do you have?
Thanks to all of you for your continuing suggestions.

I have a 1996 John Deere 6068T.

To be honest the soot problem is not all that bad. I don't see any smoke in the exhaust even at startup. Just a noticeable area of dirtiness around the exhaust. I do wonder whether the shape of the stern is creating a low pressure spot there.

I'll take before/after pictures next time I go out if I remember.

Thanks

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Old 11-30-2015, 06:20 PM   #24
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Richard,
I too have John Deere's. In my case the 6076. They don't produce noticeable soot, but after coming down from Canada (a 91 hour run) I did find that the transom was not as bright as it should be. the grey stuff doesn't want to come off with the light duty boat wash. I'm trying to find something that doesn't take too much elbow grease to remove it. I'll try some of the cleaning product mentioned in the thread--Capt Bill mentioned Sea Shield and they seem to have a soot remover that might work. I'll let you know how it goes, although it may be a while before I get back to the boat with the Holiday Season on....
curtis
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Old 11-30-2015, 06:31 PM   #25
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Richard,
I too have John Deere's. In my case the 6076. They don't produce noticeable soot, but after coming down from Canada (a 91 hour run) I did find that the transom was not as bright as it should be. the grey stuff doesn't want to come off with the light duty boat wash. I'm trying to find something that doesn't take too much elbow grease to remove it. I'll try some of the cleaning product mentioned in the thread--Capt Bill mentioned Sea Shield and they seem to have a soot remover that might work. I'll let you know how it goes, although it may be a while before I get back to the boat with the Holiday Season on....
curtis
Interesting. Let me know how it goes.

Here's my transom after about 6-7 hours of motoring - it was clean before the trip.

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Old 11-30-2015, 06:33 PM   #26
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I did check my maximum RPM - it was 2300. I am not 100% sure what the max RPM for my 1996 JD 6068T is. I think it's probably 2400. Based on the earlier post I may be slightly over propped?

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Old 11-30-2015, 07:14 PM   #27
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Originally Posted by Dawdler View Post
Richard,
I too have John Deere's. In my case the 6076. They don't produce noticeable soot, but after coming down from Canada (a 91 hour run) I did find that the transom was not as bright as it should be. the grey stuff doesn't want to come off with the light duty boat wash. I'm trying to find something that doesn't take too much elbow grease to remove it. I'll try some of the cleaning product mentioned in the thread--Capt Bill mentioned Sea Shield and they seem to have a soot remover that might work. I'll let you know how it goes, although it may be a while before I get back to the boat with the Holiday Season on....
curtis
Try Magic Eraser. It's a very mild micro-abrasive that worked like a champ on my transom. Just a bucket of water and one sponge did my whole transom. Larger boats might need 2 sponges.
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Old 11-30-2015, 08:52 PM   #28
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Richard, your peak torque for you JD is 1800 rpm, I'd clean the stern and try running at 1800 rpm and see if it still smokes. When you run at near max rpm pushing a 54' hole in the water your going to smoke a little. Be interested to see what the speed difference would be ?
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Old 11-30-2015, 10:03 PM   #29
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Painting the hull (or transom in your case) a dark green or blue should make minor soot invisible. ... But why is your engine generating smoke? My JD is smokeless regardless of RPMs.
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Old 11-30-2015, 10:05 PM   #30
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Will a diesel (mechanical or electronic) make smoke and put black soot on the transom if it has good compression and is propped to rated rpm?

I think it needs to be over fueled or have poor compression to soot the transom. Am I wrong? My own boat w about 900hrs on the engine has paint on the transom that isn't even glossy. Some PO applied it. It's never been over propped and operated almost always at 50% load .. 2300rpm. I've never cleaned the transom more than the rest of the boat and the rest of the boat has fairly good gelcoat.
MB, your engine is indirect injection aka pre-chamber, those tend to burn quite clean unless near overload.

On most other engines, they are direct injection and soot is more an issue. Not as much turbulence near injection site so mixing can be so-so or ok. Poor mixing of fuel and air, you get soot.

I have troubleshot a few of these issues: One thing I found with the turbo diesels is sometimes there were "bad" rpms and power settings to avoid. One boat with Detroits liked to run 1700 to be easy on his engines. I monitored on a test run and at 1700 they were dirty. Asked him to go to 1800 and they cleaned right up. That was the fix, 100 more turns.

On my boat, my 450 Cummins cruises nice at 1800. But it is a little sooty there. 1700, clean. 1950-2200, clean. But the boat likes 1800. So I compromise and run 1900. Almost clean there.

I could buy the 5-hole injectors for a boat buck and replace my 4-hole, but not worth it. A brush cleans the transom just fine, and in 500miles it is not horrible.

If the OP can't make full turns due to dirty bottom, that will certainly do it.
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Old 11-30-2015, 10:43 PM   #31
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Richard, your peak torque for you JD is 1800 rpm, I'd clean the stern and try running at 1800 rpm and see if it still smokes. When you run at near max rpm pushing a 54' hole in the water your going to smoke a little. Be interested to see what the speed difference would be ?
Thanks - I do run the engine at 1600-1800 rpm as my normal cruising range. I took it up to max RPM in response to the question asked in post #3 on this thread:
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You will always get some amount of soot, but how much is too much?

The first, because it's easiest, thing to check is the propping on the boat. Look up the rated full throttle RPM for your engine, then see what they actually turn at full throttle. It should be a couple hundred RPM over, let me repeat OVER, the rated RPM.

Chances are very good that you will be below the rated RPM indicating overloading of your engine, and resulting excessive soot. The solution is to have your props repitched, which sounds much more drastic than it really is.
On your speed question I make 7.9 kt at 1800 rpm using 1.4 nmpg and make 9.4 kt at 2200 rpm using 0.9 nmpg. At 1600 rpm I'm making 7.4 kt using 2.2 nmpg (that's the max speed for going to Hawaii).

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Old 11-30-2015, 10:44 PM   #32
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...
If the OP can't make full turns due to dirty bottom, that will certainly do it.
I'm scheduling a bottom cleaning and we'll see if that helps.

Richard
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Old 12-01-2015, 07:02 AM   #33
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Soot from overloading is most common on fish killers as they run WOT for a min to get up on the plane.

Cruisers that are not visibly smoking should remember there are loads of combustion by products in the exhaust , some will discolor paint or gel coat. This does not mean a bad engine.

Chemically removing the discoloration might be done at the expense of some of the surface being cleaned.

Toilet bowl cleaner is common.

Ship Shape and Bristol is fine , but there might be a price.
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Old 12-01-2015, 07:41 AM   #34
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Interesting. Let me know how it goes.

Here's my transom after about 6-7 hours of motoring - it was clean before the trip.

The soot pattern seems to indicate the air flow around the transom is stalling in that area and do the door builds up there.

Sea Shield doesn't make an exhaust remover per say that in aware of. But they do make a sealant (Exhaust Guard) that soot doesn't seem to stick to well that makes it pretty easy to wash off.

I would not use Magic Erasers on a painted hull nor on a polished and waxed gelcoat hull that is in good shape. They will dull/scratch a polished surface.

Toilet bowl cleaner will remove the ice tea colored stains from tannic acid. But not do much to remove soot from what I've seen.
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Old 12-01-2015, 09:11 AM   #35
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restricted air intake (air filters, ER intakes) as in first post
Over propped or dirty prop/bottom not reaching wot rpm
injectors and/or valve adjustment

If your air filters are clean run the boat with a engine room hatch open and see if that cures it.

My 6 cyl Volvos need all these tweeks at 105% or I get soot on my stern, canvas, cushions... what a mess. I have done everything from prop speed to new turbos, new injectors, air seps, and on and on. She turns up 50rpm more than spec and I still get some sooting after 4 hours of running. I have not tried running with the hatch cracked open a bit which is my next step. All this work has improved the exhaust significantly but it is still not right.
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Old 12-01-2015, 10:47 AM   #36
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restricted air intake (air filters, ER intakes) as in first post
Over propped or dirty prop/bottom not reaching wot rpm
injectors and/or valve adjustment

If your air filters are clean run the boat with a engine room hatch open and see if that cures it.

My 6 cyl Volvos need all these tweeks at 105% or I get soot on my stern, canvas, cushions... what a mess. I have done everything from prop speed to new turbos, new injectors, air seps, and on and on. She turns up 50rpm more than spec and I still get some sooting after 4 hours of running. I have not tried running with the hatch cracked open a bit which is my next step. All this work has improved the exhaust significantly but it is still not right.

Maybe it just is what it is. And they will never burn 100% clean.
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Old 12-01-2015, 10:52 AM   #37
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Our Willard has no soot at all. Only very slight smoke at start up.

However the engine was new less than 10 years ago and has less than 1000hrs on the clock. Propped to rated rpm of 3000.
No transom either LOL
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Old 12-01-2015, 10:59 AM   #38
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Tailpipes that submerge when under way seem to make more a mess than those that stay above water.
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Old 12-03-2015, 04:00 PM   #39
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Your rated wot rpm could be 2300 depending on your hp. They built that model in several hp ranges:
154 115 156 22.7 2300
M1 158 118 160 23.3 2400
M2 176 131 178 25.8 2400
M2 178 133 181 26.2 2500
M3 200 149 203 29.4 2500
M3 201 150 204 29.6 2600


M4 225 168 228 33.1 2600
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Old 12-03-2015, 04:24 PM   #40
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Your rated wot rpm could be 2300 depending on your hp. They built that model in several hp ranges:
154 115 156 22.7 2300
M1 158 118 160 23.3 2400
M2 176 131 178 25.8 2400
M2 178 133 181 26.2 2500
M3 200 149 203 29.4 2500
M3 201 150 204 29.6 2600


M4 225 168 228 33.1 2600
When I do a serial number search at the JD site, my 1996 engine shows up as a 6068TFM01. I can't seem find out exactly what that is from the JD site. Could it be a 6068TFM50 M1 rated engine? If it is then it's rated at 151HP and has a max RPM of 2300. It could be a 6068TFM75. The M1 rating makes sense (I think) given the expected duty cycle.

Richard
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