How Much Smoke and Oil From a Diesel Exhaust?

[R. Bush]

I was having a survey done on a boat with a Lehman 120 engine that I was considering purchasing. When they dropped the boat back in the water after the hull inspection I hitched a ride with the owner back to his slip. When the engine was first started (after hanging overnight at about 12 degrees C) there was a fair bit of black smoke and an oily slick extending back about 2-3 m from the stern of the boat. By the time we had arrived back at the slip (about a 10 minute run at cruising speed) the smoke had turned lighter and decreased somewhat, but the slick extending back from the exhaust remained.

I'm new to old trawlers and am trying to learn what is "normal". It seemed like a lot of oil in the water to me. My little 13 hp Westerbeke never left any slick in the water even when cold. The engine supposedly has about 2001 hours on the meter.

I was planning on having a mechanic do an engine inspection but decided not to bother after the survey. For future reference what should I be expecting to see from this type of engine if it is in decent working condition? What sort of things should I be looking for as a first pass inspection I can do myself before paying a mechanic several hundred dollars to confirm an engine is in good condition?

Obviously a steep learning curve here for someone moving over from a sailboat. Thanks in advance for any advice.

 

[Woodland Hills]

Are you certain that the slick was oil and not fuel? A bad injector could result in unburned fuel coming out of the exhaust leaving a sheen behind. Also the rule of thumb is that white smoke is water, blue smoke is oil and black smoke is fuel.

 

[DavidM]

Old engines, whether they are Lehman, Perkins or whatever, smoke. Lube oil smoke which is usually blueish, is almost certainly related to rings and black smoke which is usually partially burned fuel can be rings, injectors, overloading (but not in neutral at idle). Black smoke can cause an oil sheen that is difficult to differentiate from a lube oil based smoke sheen.

Running hard for a few hours can reduce it even when later started up from cold.

I suspect that the smoke you are seeing will not affect engine performance and the engine may have many thousands of hours of life left. But only you can decide if it is too much for your sensibilities.

David

 

[Ski in NC]

A 120 Lehman will smoke some at a 12C start. A bit of oil sheen then is normal too. Completely normal. Mostly due to incomplete combustion at lower temps with engine cold. The way to check this is to take the boat out and run it under at least half load for like a half hour or more, then come back to the dock and with engine hot and idling there should be almost no smoke and almost no oil sheen.

There are things that can go wrong (gear oil cooler, engine oil cooler) that can put liquid oil out the exhaust. Checking those get technical.

 

[R. Bush]

Are you certain that the slick was oil and not fuel? A bad injector could result in unburned fuel coming out of the exhaust leaving a sheen behind. Also the rule of thumb is that white smoke is water, blue smoke is oil and black smoke is fuel.

Sorry; my bad. I really couldn't tell if the slick was from oil or diesel. To me at least they would both look the same. I get that an older cold diesel will smoke some and maybe pump out a bit of "oil" at startup. I was just wondering when and if I should expect this to stop in an engine that had no real mechanical problems.

Thanks for the reply.

 

[R. Bush]

Old engines, whether they are Lehman, Perkins or whatever, smoke. Lube oil smoke which is usually blueish, is almost certainly related to rings and black smoke which is usually partially burned fuel can be rings, injectors, overloading (but not in neutral at idle). Black smoke can cause an oil sheen that is difficult to differentiate from a lube oil based smoke sheen.

Running hard for a few hours can reduce it even when later started up from cold.

I suspect that the smoke you are seeing will not affect engine performance and the engine may have many thousands of hours of life left. But only you can decide if it is too much for your sensibilities.

David

Thanks for the reply. I will be making a little "smoke color" reference card for my wallet, and taking it along for the next boat I look at.

 

[Swfla]

Both David and Ski said to run it at cruising speed load for 1/2- several hours. Seems not exact but they're both telling you to take it out and run it at cruising speed roughly 1600-1900 rpm for well over an hour. It should stop this slick from showing up afterwards. Basically a lack of use issue. If you know for a fact the current owner has been running the boat under load for several hours on a regular basis the past few months, then this "test" won't make any difference as one is assuming the engine hasn't been run loaded much lately. Maybe you can convince owner/broker to allow this. Sounds like a great idea to me as well. But you did admit that evaluating this type of engine on your own is a steep learning cove. I personally, see the value of hiring a mechanic. Hope I cleared up why and when you'd run this type test. It's just basically an attempt at "blowing out the carbon" from a granny driven vessel. If it not been driven in a granny manner, no point in doing it. It requires you to examine the current owners back story and evaluate it for truth.

 

[Comodave]

Listen to Ski.

 

[R. Bush]

Both David and Ski said to run it at cruising speed load for 1/2- several hours. Seems not exact but they're both telling you to take it out and run it at cruising speed roughly 1600-1900 rpm for well over an hour. It should stop this slick from showing up afterwards. Basically a lack of use issue. If you know for a fact the current owner has been running the boat under load for several hours on a regular basis the past few months, then this "test" won't make any difference as one is assuming the engine hasn't been run loaded much lately. Maybe you can convince owner/broker to allow this. Sounds like a great idea to me as well. But you did admit that evaluating this type of engine on your own is a steep learning cove. I personally, see the value of hiring a mechanic. Hope I cleared up why and when you'd run this type test. It's just basically an attempt at "blowing out the carbon" from a granny driven vessel. If it not been driven in a granny manner, no point in doing it. It requires you to examine the current owners back story and evaluate it for truth.

Based on a previous survey from 5 years ago the engine has been run 11 hours in the past 5 years. The owner claims they have just been too busy to use the boat, and that is the reason for selling. Based on other issues the surveyor has found I have walked away from this one. Surveys sure aren't cheap; but if you find a good one who is working for you and not the broker; they sure can pay for themselves in future money and grief saved.

 

[Swfla]

This is good news. You're listening to the surveyor and understanding that lack of use causes issues. Then you do what's right for you. You're bound to find a boat that's right for you. cheers

 

[DavidM]

In my limited experience (which is a heck of a lot more limited than Ski's) you need to run rather hard, about 200-300 rpm off of top for at least an hour for a Lehman to really blow out carbon build up, clean up the injectors which results in a semi-permanent lessening of smoke and sheen on startup as well as during normal runs.

David

 

[rgano]

I had twin 120 Lehmans. One of them developed a problem and was pulled and completely overhauled by the Ford Lehman dealer in Dan Diego. Bored with new pistons, the whole nine yards. Both engines smoked at startup before the work was done and spit out a diesel sheen. Afterwards, well, not one bit of difference. This is what they do, hot weather or cold. about twenty years later, I had a know-it-all lock tender on the Caloosahatchee lean over the wall and look at my idling 120s and tell me I needed an engine overhaul - I laughed him off.

 

[SoWhat]

A 2000 hour engine should not smoke beyond warm up.
Hold a paper towel or rag over the exhaust. If it's black and oily, then the rings or valve guides are probably worn. A rebuild is in the future.
Fuel won't be as black and will smell like diesel. Probably a clogged injector nozzle. They can be rebuilt or replaced at minor cost.

 

[rgano]

A 2000 hour engine should not smoke beyond warm up.
Hold a paper towel or rag over the exhaust. If it's black and oily, then the rings or valve guides are probably worn. A rebuild is in the future.
Fuel won't be as black and will smell like diesel. Probably a clogged injector nozzle. They can be rebuilt or replaced at minor cost.

True enough, but for myself, I am walking from any boat with a diesel doing that. Lots of other stuff might be wrong, but the power plant is not allowed to show any sign of weakness or neglect. Yes, I will pay more, but the right boat for me is the wrong boat for somebody else. Diff strokes.

 

[oscar]

I find that diesels, whether my DD's in the boat or the modern Cummins in the land yacht, wake up noticeably better with a few hours of engine heat.

 

[DavidM]

True enough, but for myself, I am walking from any boat with a diesel doing that. Lots of other stuff might be wrong, but the power plant is not allowed to show any sign of weakness or neglect. Yes, I will pay more, but the right boat for me is the wrong boat for somebody else. Diff strokes.

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

 

[Comodave]

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

+1.

 

[rgano]

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

David!
I spent 29 years with two 120 Lehmans. I KNOW they smoke at idle and clean up well underway. I think I said that here.

 

[PM]

Mine used to smoke and leave a bit of a sheen. After a total rebuild there is very little smoke at start up and none after it comes up to temp.

pete

 

[Olebird]

I think Ralph said he was moving on to the next one ... excellent decision - imho! Any internal combustion engine, kept near the water that has only seen 11 hours use in 5 years - is likely gonna be a money pit! (not to mention the rest of the boat)



Wonder when the oil was last changed??


Good luck Ralph, keep us posted on what you find.

 

[koliver]

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

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.

 

[rgano]

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'...

 

[sunchaser]

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.

 

[koliver]

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'

 

[rgano]

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.

 

[Swfla]

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.

 

[Russell Clifton]

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.

 

[Moonfish]

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.

 

[Swfla]

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?

 

[rslifkin]

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.