How Much Smoke and Oil From a Diesel Exhaust?

[Jeff F]

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

 

[Woodland Hills]

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.

 

[Swfla]

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.

 

[sdowney717]

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.

 

[rgano]

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.

 

[Group9]

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.

 

[Woodland Hills]

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.

 

[SoWhat]

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.

 

[Swfla]

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?

 

[SoWhat]

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.

 

[Swfla]

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.

I can see how the this can be confused with exhaust buildup at a glance.

 

[CruisingTheICW]

How much smoke...

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.

I’m not a diesel tech or surveyor, but I’d be concerned, too. I’d definitely be getting a knowledgeable diesel tech check it out, and have main engine and generator oil analyzed. A couple of years ago, I was getting white smoke from mine. Turned out to be an electronics issue. Through the diagnosis, I learned that smoke - black or white - can be caused by several sources.

 

[Robbc49]

Could be something else

I ran twin Ford Lehman’s (225 turbos) for an extended time. I have to say that even in cold conditions the smoke which first appeared was always either grey or white and dissipated quickly. I did however have a “slick” which started as the starboard engine began running and this slick was pretty constant. While I can’t swear it was caused by my faulty heat exchanger I can tell you that after having it repaired (had holes in it) the slick stopped. Never had another issue. I should add that it was routine for me to add oil on an ongoing basis, to both engines, sometimes daily during the Loop. But o loved the Lehmans.

 

[TollerTrawler]

Not only would I never consider buying a boat without an engine inspection, on older diesels I have oils testing done. On a recent pre-purchase inspection, the engine oil and coolant came back "green down the line." However the transmission (not even the original, a higher quality replacement) on this engine registered 9X more than 'Severe' level rating on lead detection. You can get your inspection costs recovered (and a lot more depending on the outcomes) through renegotiating the offer price. And if the mechanical doesn't find anything, you've just bought yourself a bunch of peace of mind and safe travels.

 

[Robbc49]

I agree with Toller. Having the engine survey AND oil analysis is relatively cheap insurance.

 

[ferg]

I rarely comment on here as my boat is very different to a sea going trawler (although I enjoy reading the forum), It's a 30ft river cruiser in the UK, with twin Perkins (1961 and 1962 - 4.270 naturally aspirated). But I thought I'd comment on this topic as I think it's interesting.

You would have thought a river cruiser is generally run much lighter than a sea going boat, and so their engines would smoke a lot. But these old Perkins are very smoke free. On a cold day start-up produces a bit of black smoke for 30 secs or so, but in general running there is hardly anything. After a long run you get a slight sheen on the water (I guess diesel) when idling before turning the engines off.

It's not like the engines have been treated correctly through their life either. When I bought the boat neither engine had a working thermostat. Both were jammed open so the engines took a long time to get to working temperature. I had no idea how many years they had been like that, but I suspect many. Now they get up to 84degC (sorry I'm English) quickly and stay there.

I generally run them at 1250 rpm (max rpm is 2,000). That seems to be the sweet spot with the least vibration and noise.

 

[Skip Sunnell]

Ralph,
There is a lot of good advice here. My boat has twin Lehmans with 6000 plus hours. What you describe is pretty common to me, especially if the boat has not been out of the slip and cruising for awhile.

My Lehmans don't like to sit in the slip, but when I do warm them up, I idle them above above the vibration threshold where they run smooth. These engines don't have glow plugs so on start they are running very rich and require time to heat to properly combust. I'm surprised that whomever did your survey didn't address the condition with you and/or suggest additional investigation if he/she was concerned.

I love my Lehman diesels, and put up with their cantankerous smoking when cold until they "limber up". I notice that after running at normal temperature (180 degrees) for over a half hour, shut down and start up after being on the hook, they will smoke a bit but very little, if any sheen on the water.

It might be a consideration for you to require an oil test on any boat you are considering to best determine if there is internal wearing of parts. A good surveyor will know how and who to contact for this service.

Personally, for me in the end, it was who I was purchasing the boat from and the maintenence history of the mechanics who had worked on her that helped me make my decision.

 

[jjorgenson3]

+1

 

[R. Bush]

Thanks for all the feedback everybody.

I never had an engine inspection done. There was one scheduled for after the survey, but based on deck rot problems and other issues pointed out by the surveyor, I just walked away at that point. An expensive lesson for me in the need to spend a lot more time checking out every inch of a potential boat before hiring someone else to do it.

That was the reason for my initial smoke/oil slick question. From now on I will make sure to have the engine run before a survey, and if there are smoke or oil slick present insist it be run long enough to reach operating temperature and see if the problem goes away. The impression I get from the posts here is that if it doesn't there are probably deeper issues and I should perhaps walk away at that point.

My "problem" is that I am shopping at the very bottom of the trawler market. I am looking at a price point of no more than C$40000. I know that there are some decent 30-34 ft. boats out there at that price if I am patient, but even then I am going to have to live with problems that need fixing and work to be done. I just can't afford to start off with a boat that has 15-20k of deck work that I can't do myself no matter how low the asking price.

 

[AlanT]

I will second the comment made by others - get an engine inspection! But this should be done as part of the sea trial. Here is a reason that should get your attention: I recently bought my current boat which has Detroit Diesel 8v92TA engines. I had a mechanic during sea trial. He required that the seller's broker (who was driving the boat) run the boat at full throttle for a short period of time, while he had his computer plugged into the engine electronic box. After running at full throttle for about 30 seconds, and watching temperatures etc. He commanded that we immediately shut down one engine. We did so. Later inspection revealed partially blocked cooling had indirectly led to the engine breaking piston rings and scoring cylinder liners. $68k later after the seller had the engine repaired and the cooling on the other engine also removed/cleaned and replaced I was able to buy the boat (after a second sea trial with mechanic on board). The cost of the mechanic, around $1k for the first sea trial, saved me $68k. Seller paid for second sea trial.

 

[Xsbank]

Lehmans always mark their territory on start-up. You can reduce the slick somewhat by rebuilding your injectors but it doesn't stop. In any case the interval is 1000 hours. Get a farm shop to do them, way cheaper than a marine store.

Never start your engines and allow them to idle for long periods. Start up and throw off the ropes and as soon as possible bring the rpms to about 1000 and warm the engines to normal operating range before increasing above 1200. If you can't leave yet, put them in gear at the dock but 'always' warm up with a load.

Oil in the water is a different issue, your engine is sucking lube oil and you are perilously close to a runaway. Completely different issue.

Smoking while cold is the nature of the design.

As per the manual, run it at WOT for a few minutes to blow out the carbon, heat up the oil, load up the engine so you don't glaze the cylinders by cruising it too gently for too long. WOT will also reveal any looming weakness in the cooling systems etc.