Generator Smoke and Soot Under Load

[Sababa]

My 6kw Northern Lights generator is putting out soot and gray smoke when I load it up. It’s original to my 2001 Nordic Tug and had only around 200 hours on it when I bought the boat in 2020. The generator was not running then and in pretty bad shape from barely having been used over the years. I had pretty much everything replaced—injectors, lift pump, fuel return valve, exhaust elbow, you name it. It ran great and still does under moderate loads. But since then, I’ve added a bigger (3kw) inverter charger and a small water maker that draws about 1200 watts and I’ve noticed that when I load it up with these plus the hot water heater it puts out gray smoke through the dry exhaust and soot through the wet exhaust. Even so, the generator runs smoothly and the temperature is pegged at a normal 195 degrees.

Among the potential causes that the manual identifies for this, the only ones I haven’t already addressed are engine timing and too much muffler back pressure. These seem unlikely to me, though, since the generator is running smoothly apart from the smoke and soot.

I’ve seen people say that this can be normal carbon burning off from a generator that was previously run infrequently and/or at low loads, and that the best thing I can do is to continue to load it up and let it clear itself out. If that’s so, I’d like to do it as much as I can while I am cruising. But I’m concerned that I may be doing some harm and that maybe I should run it at lighter loads where it doesn’t produce smoke and soot until I can get it looked at.

Any thoughts out there?

 

[SteveK]

Overloaded is first thought. Try no load and run for a few minutes, any smoke? Turn on one item at a time until smoke starts and you will know if too much load is issue. Once there is too much the engine sound/rpm should be noticible in a slowdown, sounds like bogged down.

 

[Sababa]

Overloaded is first thought. Try no load and run for a few minutes, any smoke? Turn on one item at a time until smoke starts and you will know if too much load is issue. Once there is too much the engine sound/rpm should be noticible in a slowdown, sounds like bogged down.

I do that, and that’s what you’d think. But when you add up the loads, they are no more than 5kw, below the rated 5.5kw output. The tone definitely goes down a note when I add the water heater (1800w) on top of the inverter charger (1800w) and the water maker (1200w), and there is no smoke or soot when I load up just two out of three. But there is no slowdown or laboring like when I’ve really overloaded it (wife turned on the toaster oven with all of those going, nearly stalled).

 

[GoneFarrell]

Pull the air cleaner, see if that effects the black smoke/soot at load.

 

[Sababa]

Pull the air cleaner, see if that effects the black smoke/soot at load.

I just replaced it before this trip, but I will pull it entirely to be sure.

 

[sunchaser]

S
Do you have a good ammeter reading out loads? Is your volt meter showing a solid 110? What is the amp rating as stated on the genset plate? At what amps does it start acting up? That number may well be your max for awhile until you double check injectors, injection pump, valves, cooling water flow and genset temps with an IR gun.

 

[twistedtree]

Tough to say, but it might be simple overloading. The 5.5kva rating is likely just that, kva, not W. It's unlikely that your total load makeup is exactly a power factor of 1.0, in other words more than the nameplate wattages.

 

[Jeff F]

I do that, and that’s what you’d think. But when you add up the loads, they are no more than 5kw, below the rated 5.5kw output. The tone definitely goes down a note when I add the water heater (1800w) on top of the inverter charger (1800w) and the water maker (1200w), and there is no smoke or soot when I load up just two out of three. But there is no slowdown or laboring like when I’ve really overloaded it (wife turned on the toaster oven with all of those going, nearly stalled).

Modern inverter/chargers like the Multiplus can be set to manage generator loads. It sounds like you're bumping against the top end of the generator capacity, and this is an easy solution.

 

[Larry M]

For what it’s worth, we had a NL 5Kw generator that had similar systems. I had serviced about everything 200 hours before I couldn’t fully load it up without smoke. I finally pulled the generator from the boat and took it to a NL dealer. They pulled the exhaust elbow and it was clogged . We were all amazed. They said typically that would have been the first thing they looked at but since it only had 200 hours, it was the last.

 

[rslifkin]

Tough to say, but it might be simple overloading. The 5.5kva rating is likely just that, kva, not W. It's unlikely that your total load makeup is exactly a power factor of 1.0, in other words more than the nameplate wattages.

It's possible, but most generator engines are a bit oversized to give good motor starting performance. So with a steady load, you'll typically run into an electrical overload (and possibly a breaker trip) before you've actually overloaded the engine (or even reached full output from the engine).

 

[cafesport]

So a couple of things stand out here. These gens need a valve lash adjustment after break in which is 50 hours. Probably never ever done. 195 is very high even in 90 degree water at full load. Check your heat exchanger bundle for impeller pieces. Lock rotor start up for your watermaker is probably 4500 watts. You need to exercise some load management in the morning if you want to run everything. Turn on the water heater last and only when the batteries stop accepting current. Fwiw the toaster shutdown your wife is trying to do will eventually cause the lift pump diaphragm to rip. Ask me how I know this.

 

[CamoPirate]

Pull the air cleaner, see if that effects the black smoke/soot at load.

Just adding a crazy story for entertainment purposes.

Delivery of a recently purchased used 75 foot multi million dollar trawler and the new owner tells us the big genset is bad, complaint is genset smokes bad under load. survey said so, mechanics best diagnosis is a bent rod and they boat bought knowing it needs a new genset.

This makes no sense to me so I go have a peak at it. Check oil and it’s way over full, check air cleaner and it’s soaked in oil..

Correct oil level, remove air filter and the genset fun’s perfect. Saved the owner buying a new 30kw genset.

Moral of the story, Don’t skip the basics. I

 

[sunchaser]

Moral of the story, Don’t skip the basics. I

This!

A dozen or so basics have been provided to the OP. Considering the age and low usage of the genset more than one may be at play.

 

[GoneFarrell]

Just adding a crazy story for entertainment purposes.

Moral of the story, Don’t skip the basics. I

Ha! Good story.
Mine: was coming out of the fog slow, entering Lopez pass into a strong ebb. Big boat to starboard wallowing around in the chop, bad place to have little helm.

Radio chat has me leading big boat in, so I add revs to lead in. Motor does not respond to increased throttle.

I look back, huge soot cloud, can barely see my own dingy! No smoke or fire in engine bay. Bad place to slow down and get run over by following boat. So I lay a smoke screen through the pass, get out of the way.

Turns out air cleaner top cover pulled down and restricted air intake a high revs. Pulled air cleaner, runs perfect. Next, fab a spacer or taller filter to fix.

 

[Sababa]

So a couple of things stand out here. These gens need a valve lash adjustment after break in which is 50 hours. Probably never ever done. 195 is very high even in 90 degree water at full load. Check your heat exchanger bundle for impeller pieces. Lock rotor start up for your watermaker is probably 4500 watts. You need to exercise some load management in the morning if you want to run everything. Turn on the water heater last and only when the batteries stop accepting current. Fwiw the toaster shutdown your wife is trying to do will eventually cause the lift pump diaphragm to rip. Ask me how I know this.

Checked the maintenance logs I inherited from the previous (original) owner, and sure enough, no 50 hour valve adjustment. It’s on the list along with a timing check/adjustment for the off season. Also going to check the muffler back pressure.

The manual says that 195 is the set point for the thermostat for this generator. I thought it was high too before I checked. I changed the impeller along with the air and fuel filter in June and had everything in the coolant pathway replaced or serviced in 2020 so I’m pretty confident that’s good.

The water maker is on an 8 amp breaker per spec so I don’t see how it could draw that kind of start up power without tripping.

My strategy in the meantime is to run the water heater and the water maker first, then switch off the water heater and turn on the battery charger once we have hot water. Otherwise we’d have to wait three or four hours for the batteries to fully charge before we could shower!

At this load, the toaster oven, microwave, or coffee maker won’t bring the genny to its knees so long as you don’t try them all at once.

As an aside, I removed the solar panel that the PO had installed to make room on the pilot house for a life raft and kayak racks and have not replaced it because I’m sure not being run enough under a good load was the source of the problems I have encountered. Though I’m rethinking that now with the Starlink flat high performance hoovering down so much juice. I upped my house bank to 880 AH and it’s still just barely enough to get me to 24 hours without going below 50% charge with the Internet turned off from 10 to 6 and a four hour generator run every morning.

 

[Turtle Blues]

All the basics have been covered above.

At 5/5.5kw you are pretty well fully loaded and seeing the results. That's the trouble with a genset, rpm is static, it can't rev up to meet the load.

 

[Sababa]

All the basics have been covered above.

At 5/5.5kw you are pretty well fully loaded and seeing the results. That's the trouble with a genset, rpm is static, it can't rev up to meet the load.

Actually, I didn’t get an answer to my initial question, which is whether the load it up and burn it out theory has any legs. Doesn’t sound like there are any buyers here.

 

[O C Diver]

Actually, I didn’t get an answer to my initial question, which is whether the load it up and burn it out theory has any legs. Doesn’t sound like there are any buyers here.

If I were going to do that (after checking everything else mentioned for the easy fix), I probably wouldn't run it over 75%. That should generate more than enough heat, without cooking the generator end.

Ted

 

[Bmarler]

Actually, I didn’t get an answer to my initial question, which is whether the load it up and burn it out theory has any legs. Doesn’t sound like there are any buyers here.

i'd try it. as has been mentioned, the engine usually has more hp than the back end can develop. with generators that have been lightly loaded more often than not, (like standby gensets) they can get some build up that should be burned out by loading heavily for a time. i'd run it hard for an hour and see if it cleans up. just keep an eye on the temperature gauge while you do it. and if you have an ir temp gun shoot the back end to see if it's heating up.

 

[Bmarler]

If I were going to do that (after checking everything else mentioned for the easy fix), I probably wouldn't run it over 75%. That should generate more than enough heat, without cooking the generator end.

Ted

do you think 75% for the engine equals full output for the back end? (more or less?)

 

[SteveK]

Actually, I didn’t get an answer to my initial question, which is whether the load it up and burn it out theory has any legs. Doesn’t sound like there are any buyers here.

My manual suggests starting and running without load before adding load.
Then for shutdown, remove load and let run before shut down.

So no legs for load it up to clear it here.

 

[Turtle Blues]

Personally not a fan of the "Burn off the carbon" theory. Think it was promoted by an engine re-builder. It's not smoking in the mid-range, only under heavy load which in incomplete fuel burning. It's not "removing deposits" that term goes with fuel additives which can cause a whole other set of problems if over used.
My preference would be to run in the comfort range with a little load management or look at a larger unit.

 

[KnotYet]

(edit)
The water maker is on an 8 amp breaker per spec so I don’t see how it could draw that kind of start up power without tripping.
(edit)

That breaker seems quite low rated for the W/M you say uses 1200 Watts.
1200W@120V would seem to draw 10A and should be on a 15A or so breaker.
As cafesport says, the startup demand could be 3-4x the running wattage.
It could be that 1200W is the startup demand and the running is somewhat lower.

Also I wouldn't even use the generator before at least checking that valve lash.

 

[Sababa]

That breaker seems quite low rated for the W/M you say uses 1200 Watts.
1200W@120V would seem to draw 10A and should be on a 15A or so breaker.
As cafesport says, the startup demand could be 3-4x the running wattage.
It could be that 1200W is the startup demand and the running is somewhat lower.

Also I wouldn't even use the generator before at least checking that valve lash.

My mistake, the watermaker (FCI Aqualite) only draws 600W.

 

[Jeff F]

For what it’s worth, we had a NL 5Kw generator that had similar systems. I had serviced about everything 200 hours before I couldn’t fully load it up without smoke. I finally pulled the generator from the boat and took it to a NL dealer. They pulled the exhaust elbow and it was clogged . We were all amazed. They said typically that would have been the first thing they looked at but since it only had 200 hours, it was the last.

I've had that happen on small Yanmar auxiliaries. When it happens the water coming out is black at all speeds, and exhaust is black at higher speeds.
That sounds consistent with the OP's description.

 

[Sababa]

I've had that happen on small Yanmar auxiliaries. When it happens the water coming out is black at all speeds, and exhaust is black at higher speeds.
That sounds consistent with the OP's description.

The exhaust elbow was completely clogged when I bought it and I replaced it with the stainless steel one they spec on the new models. I don’t have any soot in the water or smoke at lower loads. I’m just going to take it easy and manage my loads until I can get the valves adjusted when I’m back in port. Thanks everyone for the advice!

 

[sunchaser]

My mistake, the watermaker (FCI Aqualite) only draws 600W.

S
Start thinking amps, not watts. How many amps is scribed on the genset. Your panel ammeter will tell you how loaded the genset is with various items turned on. And is your panel voltmeter telling you you’ve got 110?

 

[O C Diver]

do you think 75% for the engine equals full output for the back end? (more or less?)

Depending on ambient temperature, I don't want to see the generator end running at continuous full output. I have no idea how clean the windings and cooling passageways are. Really doubt full rating is required to heat the engine up enough.

Ted

 

[Sababa]

S

Start thinking amps, not watts. How many amps is scribed on the genset. Your panel ammeter will tell you how loaded the genset is with various items turned on. And is your panel voltmeter telling you you’ve got 110?

My panel just has a volt meter. It reads a hair above 120.

 

[Barking Sands]

You can do an easy check right away. Get a meter..set to Hertz, stick both probes in a plug socket and measure hz at no load. Should around 62.5 or so. Check you manual for settings. Then load it up hard and check again. Should be just under 60. Maybe 59.5. Again check manual. Hz directly correlates the engine rpm with 60 hz being 1800 rpm. If you are getting a huge sag under load you may need to set the throttle range. Thats usually an easy adjustemt. If the swing between no load 62.5 and big load is more than about 3 hz then that may indicate engine issues like the valve adustment. Obviously its not fuel since its black exhaust.