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Old 09-11-2020, 09:47 AM   #21
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Rich:

Your engine, a Yanmar 6LP I believe, is a generation newer than the Lehman discussed here. The Lehman smokes. Your Yanmar 6LP smokes less. Newer common rail injected engines smoke even less. There is nothing wrong with an older engine smoking. It is the nature of the beast.

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It is all about injection pressure. Don't quote me on the numbers here, but:
any engine designed before 1980 will have injection pressure below 1000 psi. Any designed with the next level of EPA rules will have higher pressure, say up to 3000 psi, then another level of EPA rules sent them soaring, into the +20000 psi range, common rail designs, etc. Tier III is the present level, for which I don't know the pressure. Each increase in injection pressure results in less particulate emission (smoke), more complete combustion, less NOx, etc.
Most of us are stuck in lower injection pressure engines, so expect some smoke.
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Old 09-11-2020, 10:05 AM   #22
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Originally Posted by koliver View Post
It is all about injection pressure. Don't quote me on the numbers here, but:
any engine designed before 1980 will have injection pressure below 1000 psi. Any designed with the next level of EPA rules will have higher pressure, say up to 3000 psi, then another level of EPA rules sent them soaring, into the +20000 psi range, common rail designs, etc. Tier III is the present level, for which I don't know the pressure. Each increase in injection pressure results in less particulate emission (smoke), more complete combustion, less NOx, etc.
Most of us are stuck in lower injection pressure engines, so expect some smoke.
I witnessed the pop test of my Ford Lehman 120 injectors where they popped at around 2700 PSI. Just sayin'...
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Old 09-11-2020, 10:12 AM   #23
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The OP said 11 operating hours in 5 years because they didn't have the time. For me, that would be a walk away situation before survey, likely indicating other marine trouble spots that could appear.
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Old 09-11-2020, 11:55 AM   #24
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I witnessed the pop test of my Ford Lehman 120 injectors where they popped at around 2700 PSI. Just sayin'...
But you don't say when your engines were designed. FL likely kept to the existing standards for injection pressures.

I too witnessed the pop test on my TAMD41s in 2000, engines built in 1990, which popped at 1500 PSI. No idea when they were designed.

The original TMD40s, 1979 engines, designed decades earlier, were smokier, due to lower injection pressures.

More current designs pop at over 20000 PSI and emit no smoke at all.

Just sayin'
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Old 09-11-2020, 01:18 PM   #25
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But you don't say when your engines were designed. FL likely kept to the existing standards for injection pressures.

I too witnessed the pop test on my TAMD41s in 2000, engines built in 1990, which popped at 1500 PSI. No idea when they were designed.

The original TMD40s, 1979 engines, designed decades earlier, were smokier, due to lower injection pressures.

More current designs pop at over 20000 PSI and emit no smoke at all.

Just sayin'
The FL 120 was designed way back just after horses stopped pulling trolleys I think, My were in a 1972 GB 42 and probably built in 1970-71.
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Old 09-11-2020, 01:35 PM   #26
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So, the OP walked on this boat. I agree with the assumption, that such little use is likely to manifest itself in problems with other areas of the boat and smart to walk away.His surveyor confirmed other issues. My question is: about engines that have been run at low load and have carboned up because of this; will running them for several hours to blow out the engines "solve" that one issue or is there lasting engine damage.
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Old 09-11-2020, 01:41 PM   #27
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If you run into this issue again, insist that the sea trial be done before the haul out and be a long enough trial that the problem could resolve itself.
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Old 09-11-2020, 01:58 PM   #28
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A local mechanic here calls it "blow by", which he says is completely normal for Lehmans. Our little fuel slick is much more noticeable during start/warm up. Much less after running at temp and load for some time.
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Old 09-11-2020, 02:02 PM   #29
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If you run into this issue again, insist that the sea trial be done before the haul out and be a long enough trial that the problem could resolve itself.
That's another intelligent way to go about looking at used boats but doesn't answer the question: does grannie driving, low load, that creates carbon buildup cause any long term engine issues assuming that a good hard run blows out the carbon and cleans up the exhaust?
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Old 09-11-2020, 02:05 PM   #30
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That's another intelligent way to go about looking at used boats but doesn't answer the question: does grannie driving, low load, that creates carbon buildup cause any long term engine issues assuming that a good hard run blows out the carbon and cleans up the exhaust?

It depends on how long term, how much sitting it did in addition to just low load running, and it depends on the engines too. Some engines are much more sensitive to under-loading than others, and some need longer periods at high load to get the oil hot enough to get rid of condensation, while others get warm enough even at light load.
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Old 09-11-2020, 02:05 PM   #31
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So, the OP walked on this boat. I agree with the assumption, that such little use is likely to manifest itself in problems with other areas of the boat and smart to walk away.His surveyor confirmed other issues. My question is: about engines that have been run at low load and have carboned up because of this; will running them for several hours to blow out the engines "solve" that one issue or is there lasting engine damage.
I just bought a boat with a 15 year old 1700 hour motor that has always been run at low load. High load performance was poor until I ran for a few hours in the higher range, and now it appears to behave perfectly. My working theory is that I cleaned out carbon buildup in the exhaust around the water injection.

If in doubt consult with a real mechanic :-)
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Old 09-11-2020, 02:28 PM   #32
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I just bought a boat with a 15 year old 1700 hour motor that has always been run at low load. High load performance was poor until I ran for a few hours in the higher range, and now it appears to behave perfectly. My working theory is that I cleaned out carbon buildup in the exhaust around the water injection.

If in doubt consult with a real mechanic :-)
Or you burned the soot and slobber off the turbine side of your turbocharger to bring it’s efficiency back to normal.

Soot buildup on the blades changes the shape of the airfoil lowering the speed at which the turbine spins the compressor side. This will lower the amount of charge forced into the cylinders at a given RPM compared to a clean turbine reducing hp.

This is why we did periodic internal engine washes using “gas path cleaner” when I was a helicopter mechanic. On the oil rigs offshore in the Gulf of Mexico, this was done daily with clean freshwater due to the salt vapor in the air.
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Old 09-11-2020, 02:29 PM   #33
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I realize that there's no simple answer to the question. It does appear that this engine situation is reversible. If only those other time/neglect issues could be resolved as easily. Personally, I'm not a gambler and would prefer to buy a boat that has been used and maintained on a regular basis. It may have a higher price tag but in the long run, likely to cost less in money, time and aggravation.
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Old 09-11-2020, 03:47 PM   #34
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What happens if a water LEO - USCG personnel happen to be walking down the dock and sees your sheen on the water? Do you tell them it always does that it is normal? I dont see other boats leaving sheens on the water at marinas, not that it does not happen. Get out the dish soap...If I was looking at a boat to buy and it had visible oil sheens in the exhaust water, that would prevent me from buying it. My own boat does not do that, but it is gas powered.

Worst one I saw was a twin engine DD owner ran his engines for couple hours in his slip and there was thick soot floating everywhere over the entire marina. Soot though I dont know if that is a violation.
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Old 09-11-2020, 04:10 PM   #35
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What happens if a water LEO - USCG personnel happen to be walking down the dock and sees your sheen on the water?
For a properly running older engine design like FLs, the sheen isn't big enough to raise alarms.
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Old 09-11-2020, 04:16 PM   #36
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Originally Posted by DavidM View Post
Rich:

Your engine, a Yanmar 6LP I believe, is a generation newer than the Lehman discussed here. The Lehman smokes. Your Yanmar 6LP smokes less. Newer common rail injected engines smoke even less. There is nothing wrong with an older engine smoking. It is the nature of the beast.

David
We have twin Yanmar 6LYA's with 400 hours. They have always black smoked just a little bit until they are warmed up and then it goes away. Usually about five minutes to ten minutes or so, depending on how quick they are loaded and hit operating temperature.
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Old 09-11-2020, 04:31 PM   #37
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What happens if a water LEO - USCG personnel happen to be walking down the dock and sees your sheen on the water? Do you tell them it always does that it is normal? I dont see other boats leaving sheens on the water at marinas, not that it does not happen. Get out the dish soap...If I was looking at a boat to buy and it had visible oil sheens in the exhaust water, that would prevent me from buying it. My own boat does not do that, but it is gas powered.

Worst one I saw was a twin engine DD owner ran his engines for couple hours in his slip and there was thick soot floating everywhere over the entire marina. Soot though I dont know if that is a violation.
Running a Detroit in neutral will not get it up to temp and the smoke will not stop. This was a waste of time: they need to be over 1500rpm or so with a load to get hot enough to burn clean.
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Old 09-11-2020, 06:55 PM   #38
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Any older diesel engine will exhaust a fair amount of unburned fuel oil and unburned lubricating oil until operating temperature is reached. Once operating temp is reached, most engines will clean up. I doubt that 10 min of operation using sea water heat exchanger will bring an engine up to operating temp.

A properly running diesel can idle forever without sooting up. If run short distances at cold temp, or is not maintained, a diesel will soot up the exhaust system very quickly and will then start carbonizing the combustion chamber.

Once coked up, you need to remove the heads and chip it out. It would take 4-6 hours at temps exceeding 900F to burn the coke out. Analogous to your oven cleaning cycle. Simply running it periodically at high rpm for 15 or 30 min will clean the soot out of your exhaust, but will not clean a coked combustion chamber.

Frequent oil changes, setting valve lash, and keeping engine at operating temp will minimize soot particles. An analysis of exhaust gas and lubricating oil will give you data on what is going on. For example, Diluted lube oil would indicate rings are worn. Lube oil in exhaust might point towards valve guides or seals.
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Old 09-11-2020, 07:04 PM   #39
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Any older diesel engine will exhaust a fair amount of unburned fuel oil and unburned lubricating oil until operating temperature is reached. Once operating temp is reached, most engines will clean up. I doubt that 10 min of operation using sea water heat exchanger will bring an engine up to operating temp.

A properly running diesel can idle forever without sooting up. If run short distances at cold temp, or is not maintained, a diesel will soot up the exhaust system very quickly and will then start carbonizing the combustion chamber.

Once coked up, you need to remove the heads and chip it out. It would take 4-6 hours at temps exceeding 900F to burn the coke out. Analogous to your oven cleaning cycle. Simply running it periodically at high rpm for 15 or 30 min will clean the soot out of your exhaust, but will not clean a coked combustion chamber.

Frequent oil changes, setting valve lash, and keeping engine at operating temp will minimize soot particles. An analysis of exhaust gas and lubricating oil will give you data on what is going on. For example, Diluted lube oil would indicate rings are worn. Lube oil in exhaust might point towards valve guides or seals.
Thanks for sharing your knowledge. I wasn't aware of the two types of buildup. The exhaust buildup is what other's have been referring to. The combustion coking is obviously a more difficult buildup. What kind of symptoms develop from the coking?
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Old 09-11-2020, 07:30 PM   #40
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Thanks for sharing your knowledge. I wasn't aware of the two types of buildup. The exhaust buildup is what other's have been referring to. The combustion coking is obviously a more difficult buildup. What kind of symptoms develop from the coking?
Smoky exhaust and trailing oil slick that won't clean up after operating temp is reached. First step is determining whether it is fuel oil or lube oil. Eventually efficiency and performance will take a dive.

If hardened coke particles drop off and lodge in a ring then mechanical damage could occur.
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