Lehman 120 exhaust

Last Sunday I had to take the boat of of the boatshed she was in for the winter so I decided to go for a slow spin around the bay. About maybe 15 minutes into the run I noticed the exhaust go from its usual steamy white vapors to much darker dark gray colour which seemed to stick around longer than the usual vapors. As soon as I noticed the changed I brought the throttle down and the dark exhaust didn't show up. I decided to head back to port fearing a breakdown (single engine). I was able to get a lighter shade of gray on the way back, at higher rpms, around 1800rpm. The engine was only running at about 1800rpm when it started to produce the darker exhaust. I will try to get a picture I took of the lighter gray exhaust but the ones I have aren't that good.

About a week before moving the boat I had my had the oil changed out of my FL120, as well I had the impeller changed and the injector pump oil changed. We ran the engine for a little after changing the oil but not under load. I am just curious to see if any of you maybe able to suggest a possible cause or even say whether this is a serious problem or a normal thing. In all time using the boat I have never seen this happen before. All gauges seemed to be reading what they always read at those rpms.

I will be consulting the mechanic who did the work as we were going to sea trial and test the rpm's anyway at a later day and after purchasing a new water pump cover plate.

Thanks

What rpm can you achieve at wot? You might be over propped and loading the engine up, hence the black smoke?

Well after a few fuel lift pump fixes I did manage to get the engine to 2300 rpm last season-but can't guarantee it as I was only going by what the gauge tells me. We have had a 4 blade prop on there since we bought the boat and never had this happen, perhaps I may have put too much load on the engine before it was ready to take 2/3 throttle.

Perhaps a bit of growth on the prop?

Greetings,
Mr. V. I'm just a bit confused here. You report both a lighter and darker grey exhaust @ 1800 RPM. When was the last time you had the injectors serviced? Has the prop been changed?

If engine has been started and idled a lot without being under load (typical winter), then the first time engine is under a load it will "cook out" a bunch of oily gunk that accumulated in exhaust manifold. Typically this burns off in a few minutes and is completely normal. Smells like hot burning oil.

How long did you let it run under load?

If engine has been started and idled a lot without being under load (typical winter),

Bad,Bad,Bad,Bad,Bad,Bad,Bad,Bad,Bad,Bad,Bad,Bad,Bad,Bad,Bad,

Following Da Book from the engine builder will usually have a procedure to pickle the engine if idle over 30 days.

RF I have not had the injectors serviced, and the exhaust was most certainly a grey colour but darkness did very, it could have been cleaning up but still seemed to exist for the entire time we were running at 1800rpm.

Ski in NC, it didn't seem to be oily but perhaps I just couldn't see the slick as the boat was moving. We were under load for maybe about 30-40 minutes but not at 2/3 throttle for all of that time.

FF the last time it was under load was in December but ran at low rpm to it reached about 100C. It seems like there is a lot of debate over engine warming during the winter.

What would cause the build up of oily junk in the manifold? Would this not get flushed out anyway even at a low idle!

What would cause the build up of oily junk in the manifold? Would this not get flushed out anyway even at a low idle!

The rings require a heavy combustion load to seal ., winter ideling does not do the trick.This puts unburned fuel (incomplete combustion) out the exhaust and down into the lube oil, past the rings..

I suggest you take the boat out for an hours run , operating on the higher side of the power band, 1800rpm+.

If the engine is fine on return , have the oil changed , while its warm.

The next day , start the COLD engine and observe the smoke at start and how fast it clears OPERATING UNDER LOAD, not ideling in the slip.

Good info stated here. Let me throw in info on a repair on a later model, 5000 hour Toyota 13Z inline 6 cylinder diesel we recently completed on an 8000# capacity forklift. Operator complained of excessive black smoke, though the engine ran well. Under a light load, at around 1200-1500 RPM it was obvious. No electronics. We replaced the inner air filter, then fuel filter, no help. We then pulled the injector nozzles and had them tested at Kent's Diesel. All were great. Ronald Kent mentioned that air restriction could also be caused be intake OR exhaust valves not opening enough. We had already planned on setting the engine valves, which we did. Problem solved. This was a first for me.

I have an update to this thread. I took boat out today for a good 2 hours. I ran it at low speed for about 20 minutes, then cruise rpm for most of trip. On the last leg of the trip I opened the throttle up. I took pictures of the "cloud".

As soon as the engine was under some load and around 1200rpm This is what I got.



It cleared up after about 10 minutes and for most of the outing the exhaust look like this



Then mid journey the engine started to put this blueish stuff out and it really smelt like oil. Engine was at about 1900rpm.



Finally when nearing the marina I had the engine at WOT, I don't I have seen so much steam/vapors ever.



So I believe the dark exhaust was just built up junk burning off or burning a little excess oil as it may have been slightly over filled when changed, but in the end it seems to have cleaned up.

Looks a lot like steam in the exhaust. Some is normal depending on sea temp and atmospheric conditions, but a lot may indicated some clogging in sea water path through engine: clogged HX, gear cooler, vanes off impeller, clogged strainer, etc, etc. High wet exhaust temp makes steam out the tailpipe, and that is different from smoke as steam dissipates 10-20feet behind boat. Smoke leaves a persistent cloud way back. Nothing in pics indicates a sick engine, which is good.

Check the temp of the wet exhaust pipes, 20F above sea temp is sorta normal, 50F above sea temp is indicating reduced sea water flow.

A little "cooking off" is normal, giving that smell. Rest easy with this, worst case is cleaning the sea water flow path, which we all need to to from time to time.

Ski in NC said:

Looks a lot like steam in the exhaust. Some is normal depending on sea temp and atmospheric conditions, but a lot may indicated some clogging in sea water path through engine: clogged HX, gear cooler, vanes off impeller, clogged strainer, etc, etc. High wet exhaust temp makes steam out the tailpipe, and that is different from smoke as steam dissipates 10-20feet behind boat. Smoke leaves a persistent cloud way back. Nothing in pics indicates a sick engine, which is good.

Check the temp of the wet exhaust pipes, 20F above sea temp is sorta normal, 50F above sea temp is indicating reduced sea water flow.

A little "cooking off" is normal, giving that smell. Rest easy with this, worst case is cleaning the sea water flow path, which we all need to to from time to time.

Click to expand...

Well that is assuring I am still going to take the mechanic out anyway.
I know I don't have vanes off the impeller (brand new) and the strainer is clear but there is a good chance that the thru haul is partially blocked. I guess its time to get batteries for my infrared gun.
thanks