Generator randomly shuts down

Some generator/engineering/diesel mechanic guru thoughts would be appreciated.

We have a Northern Lights 16kw generator with about 6000 hours on it. It was well-maintained by previous owners, starts easily, and will power our three a/c zones, two refrigerators, and hot water heater simultaneously with no problem.

About three weeks ago, we did a week-long cruise in Florida waters and ran the generator to power the a/c during most of the trip. It ran normally.

A week ago, we filled up our fuel tanks at our marina. They pride themselves on clean fuel. As is our usual procedure, we gave each tank a maintenance dose of Biobor JF before fueling.

A few days later, I changed the oil in the generator, changed the oil filter and the fuel filter. Afterwards, I started and ran the generator for about 20 minutes. All went normally. The oil level is between the marks on the dipstick.

Last weekend, we did an overnight trip. The generator started easily, had good water flow out the exhaust, and was running when we left the dock. About an hour later, we discovered it had shut itself off while we were underway. I checked the strainer and it was clean. It restarted easily and the gauges showed normal loading, normal temp, and normal oil pressure. The exhaust water flow continued to be excellent. About an hour and a half later, it spontaneously shut itself off again.

The spontaneous shutdowns continued at random intervals throughout the evening and through the night, never running more than 3.5 hours before shutting itself off. It always restarted easily and the gauges always showed as normal. There was no pattern to the shut down timings. The next morning, we restarted the generator and it ran normally for the six hours or so that it took us to get home and docked.

The mains ran normally so we weren't really suspecting dirty fuel. The Racors are clean.

From an engineering perspective, diesels need clean air, clean fuel, and compression and they'll pretty much run forever. Of course, it gets more complicated when you start adding electronic sensors and such. We have good water flow and good coolant temps. The amp meter shows it's under a medium load around 12 kw. I suppose it could be a loose or bad connection at a sensor... maybe?

We're stumped. This weekend, I plan to pull off the water pump cover to check the impeller and pull off the heat exchanger end cap to look for anything unusual but, honestly, I'm not expecting to find any surprises.

Any ideas?

Thanks.

John

You may want to check into the stop switch, check the resistance to make sure it's not failing. They're typically a momentary NC switch that opens when you operate the switch. There's likely a second switch near the genset that duplicates that function. If those switches are not making good contact, they could be heating up and creating a situation where there's enough resistance to drop out the holding circuit that keeps the engine running. Any one of the engine safety controls are daisy-chained in that circuit and poor connection or a failing safety switch could be at fault. I'd check the exhaust temp switch at the exhaust manifold, pull one lead and check with an ohmmeter, it should be no or low resistance, tap on it and see if it wavers. Check the connections to all those switches, a loose spade terminal could be the culprit. A PITA, but if you can check those switches as soon as it shuts down, you may be able to get some clue as to which switch is opening, that'll go a long way in pointing you to the solution.

I've fixed several NL gennies that had a failing DC control breaker. Wires vibe in the control box and connections get loose on the breaker, or the breaker gets damaged from the vibes. Result is random shutdowns. Check that first.

Also look in the box for any other loose connections.

Some great suggestions, guys. Thanks! Now I have a place to start.

There are a few other threads on this problem so a search will provide all types of suggestions. We have a 12k NL and had similar issues. Troubleshooting:

Check wire connections to alternator, starter, sensors and fuel solenoid. The smaller control system wires can vibrate loose.

I changed the fuel solenoid but don’t think that was the problem. You can hear/feel it activate when pushing the bypass switch. Also purchased spare sensors but they seem to be OK so have not replaced them.

Fuel supply and return checked OK. Have changed generator and Racor filters recently.

Water flow, coolant level and temps were OK. Checked with IR gun. You probably know not to crank for too long if the engine does not start - problems with battery, starter and water backing into exhaust manifold.

Purchased spare sensors online through eBay or from Diesel Parts Direct. Changed the raw water pump due to shaft seal leak. Ordered by eBay from the UK, significantly lower cost than I could find in US but took a few weeks for delivery.

The most prevalent problem was (is) the control relays vibrate loose in their sockets. The 12K has four cube relays (start, preheat, bypass, run) which use sensor and switch inputs to enable start, run and shutdown states. When one vibrates loose the engine will shutdown and/or not crank. I have reseated them, moved them from socket to socket, and replaced them. I wedged them in with a small piece of wood and rubber strip. This holds for several days but eventually loosens.

We have been running it 2x1hr every day for the last six months and have always managed to start and run.

Good luck.

DCDC said:

The most prevalent problem was (is) the control relays vibrate loose in their sockets. The 12K has four cube relays (start, preheat, bypass, run) which use sensor and switch inputs to enable start, run and shutdown states. When one vibrates loose the engine will shutdown and/or not crank. I have reseated them, moved them from socket to socket, and replaced them. I wedged them in with a small piece of wood and rubber strip. This holds for several days but eventually loosens.

We have been running it 2x1hr every day for the last six months and have always managed to start and run.

Good luck.

Click to expand...

Well, that's an interesting solution. And good information. Seems to support what others are suggesting, too. Thanks.

Ski in NC said:

I've fixed several NL gennies that had a failing DC control breaker. Wires vibe in the control box and connections get loose on the breaker, or the breaker gets damaged from the vibes. Result is random shutdowns. Check that first.

Also look in the box for any other loose connections.

Click to expand...

The "joyful" part of this is going to be the difficulty reaching the box, to begin with. That end of the generator is buried in the corner of the engine room. The most visible part is the breaker reset switch on the backside of the box. It can only be seen with a flashlight from a certain angle. You can reach it only by feel; it can't be seen when your arm is in there. It's going to be fun getting that part of the housing off to get to the backside of the box. But I shall persevere and find a way!

Does the engine stop quickly or does it sputter for a few seconds before it dies. If it sputters it might be a sign of a faulty fuel pump or loose wiring to the fuel pump.

tiltrider1 said:

Does the engine stop quickly or does it sputter for a few seconds before it dies. If it sputters it might be a sign of a faulty fuel pump or loose wiring to the fuel pump.

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Hey TR,

No sputtering. It shuts down quickly. The more I hear, the more it's starting to sound like an electrical issue, like a loose relay or wire.

John

I think Ski nailed, as usual. The DC control breaker in those gen sets frequently become intermittent over time and exhibit the exact symptoms you are seeing. It's labeled "fuse" at least on some of the gen sets, which creates confusion.


Once you gain access, the connecting wires have typical spade lugs. Pull the wires off and connect them to the blades and an automotive fuse of similar rating. The wires should push right on. Then tape it up or otherwise protect the terminals from making contact with other things in the control box.


I'll bet you a beer that it will work fine after than, and you can order a replacement circuit breaker at your convenience.

twistedtree said:

I think Ski nailed, as usual. The DC control breaker in those gen sets frequently become intermittent over time and exhibit the exact symptoms you are seeing. It's labeled "fuse" at least on some of the gen sets, which creates confusion.


Once you gain access, the connecting wires have typical spade lugs. Pull the wires off and connect them to the blades and an automotive fuse of similar rating. The wires should push right on. Then tape it up or otherwise protect the terminals from making contact with other things in the control box.


I'll bet you a beer that it will work fine after than, and you can order a replacement circuit breaker at your convenience.

Click to expand...

That's a pretty brilliant diagnostic step. Thanks. I'll give that a try this weekend.

John

CaptJohnEasley said:

That's a pretty brilliant diagnostic step. Thanks. I'll give that a try this weekend.

John

Click to expand...

Don't credit me. I got it from one of the Northern Lights guys.

twistedtree said:

Don't credit me. I got it from one of the Northern Lights guys.

Click to expand...

My statement still stands, regardless from whom it came. ?

CaptJohnEasley said:

Hey TR,

No sputtering. It shuts down quickly. The more I hear, the more it's starting to sound like an electrical issue, like a loose relay or wire.

John

Click to expand...

I was about to suggest a bad seal on the fuel filter at the engine but you say it shuts down with no struggling to run issues. I too agree that it sounds like an electrical issue. I bet it will be a simple fix when/if it's found.

i agree with the above. check the thing ski said first if that doesn't pan out check the safeties for oil psi, water temp, ect. i have more than a few cause random shutdowns on big gens.

This may be pertinent based on discussion.

https://www.northern-lights.com/med...acing_22-68007_circuit_breaker_on_M_NL673.pdf

Cigatoo said:

This may be pertinent based on discussion.

https://www.northern-lights.com/med...acing_22-68007_circuit_breaker_on_M_NL673.pdf

Click to expand...

In the pictures, it's the red push-button breaker that's the DC control breaker. That's the one that can fail in a way that causes seemingly random shutdowns.

I was getting mentally geared up to disassemble the frame of the sound box and remove a cooling fan in order to crawl far enough back into a hole to get to the screws on the J box and open it up to check out the relays and the DC control breaker.

Before doing that, I had a sudden inspiration to call Northern Lights and ask them about the situation. I spoke to a guy named Joe at their Ft Lauderdale office. He listened carefully and said what they were seeing on these random, intermittent shutdowns is a failing coolant temperature switch. He said the temperature sender will still be good and the gauge will show it's within normal operating temps but the switch will randomly kill the engine. He said they've seen it frequently. The switch is on the front and much easier to access.

I mentioned the DC breaker maybe being the source and he said it was possible but they had seen far more temperature switches as the issue.

I've decided to give that a try... partly because Joe was so confident in what he was saying and partly because it's easier to get to. I'll report back on the results.

John

Fingers crossed.

Hi John,


A bit late to the party but here's one other simple thing to try if the coolant temp switch is not the problem. I had very similar symptoms with my NL 5 kW generator stopping randomly. It would start normally and then run for a while and then die. As time went on the periods of "on" became shorter until it would not even start.



The culprit was the foam air filter. It had been deteriorating over time and was clogging the air intake. I removed it, used a shop vac to clean out all the bits from the airbox I could reach and installed a new filter that I had. Working great now!


NL recommends annual removal of the foam air filters and washing in warm water and dish soap. Like twistedtree, if it helps don't thank me, we both have the same source at Northern Lights!


~Christopher

FlyFast-Boat Slow said:

Hi John,


A bit late to the party but here's one other simple thing to try if the coolant temp switch is not the problem. I had very similar symptoms with my NL 5 kW generator stopping randomly. It would start normally and then run for a while and then die. As time went on the periods of "on" became shorter until it would not even start.



The culprit was the foam air filter. It had been deteriorating over time and was clogging the air intake. I removed it, used a shop vac to clean out all the bits from the airbox I could reach and installed a new filter that I had. Working great now!


NL recommends annual removal of the foam air filters and washing in warm water and dish soap. Like twistedtree, if it helps don't thank me, we both have the same source at Northern Lights!


~Christopher

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Hey Christopher.

Good tip. Thanks. Cleaning the air filter is a good standard maintenance item, anyway.

As it turns out, we got the temp switch but ran out of time to install it last weekend before our guests arrived. We went out for a cruise Sunday and the generator ran flawlessly for ten straight hours. One of the mysteries of life.

I will be sure to clean the foam air filter as soon as possible. This boat and this generator are still new to us. As I recall, the filter is located on top, behind the heat exchanger, under a metal box or plate held down with four bolts. That part of the sound box is in a hard to get at spot, not easy to remove the top. Can the bolts and cover be removed and the filter removed from the side with the sound box top in place? There is probably three inches of clearance between the top of the engine and the roof of the sound box. I can barely squeeze a forearm in there. Do I need more room to get the air filter out?

Thanks.

John

Had same problem with my NL Genset. Took awhile, but finally, the supply water hose got old and collapsed after usage. Made Genny run hot and it automatically shuts off. Just replace hose, and all is well. Hope this works for you.

wrm95 said:

Had same problem with my NL Genset. Took awhile, but finally, the supply water hose got old and collapsed after usage. Made Genny run hot and it automatically shuts off. Just replace hose, and all is well. Hope this works for you.

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We wondered about that but ours always has good water flow, even when shutting down, and temp is always in the normal range.

John

I chased an identical problem on our NL 16KW gen for 18 months. Finally posted here, and had my solution in a day. In my case it was the resettable fuse that I think Ski is talking about. I just jumpered around it initially, and since that solved the problem, I got a new fuse. That was well over a year ago and no problems since.

Following closely as I just had a genny problem on my 15kw Onan (Cummins)...

A week ago I shut it down after noticing less water output and steam flashing indicating higher exhaust temps (at least in my mind). I pulled the intake pump and found the impeller in bad shape as anticipated.

I had a spare impeller from PO as this is a new-to-me boat, and I changed it out and fired up to normal operation. Being dockside on shore power, I switched the load gradually to genny and let it test run with full loads for about 20 minutes and all seemed normal. As a side note... although this Onan has oil pres., temp., and DC volt guages on both the genset in the ER and on remote panel in main AC/DC panel, the temp guages do not work on either.

So the other day, we left for an all day cruise and all was working fine as usual, both ac's running, full size fridge, ice maker, water heater... and for about 7 hours nothing unusual. I think I looked over the port side a thousand times watching water/exhaust flow...

At some point, in the last 45 minutes of the cruise, she stopped. I was not aware until I went down below while underway and noticed no ac working.

I have yet to be able to start any troubleshooting at all due to having company at the time and started work the next day. Thursday is my day off so will start checking into things, and am glad this thread started as there are some great ideas here. I haven't even tried a restart, as I haven't had a chance to break down the sound box for even a 1st step visual check of things.

Sorry for any derail/hijack of your thread, OP... glad there's so much knowledge here to tap into. I have no problem starting a separate thread after initial observations if that is the proper thing to do.

Thanks, and good luck getting to the bottom of it OP...

Although I feel sure earlier suggestions will lead you to your solution, I have one more thing to say regarding summer heat. My little bitty 3.5 KW generator runs my 13.5 KBtu rooftop and my 10 KBtu marine ac units simultaneously at 80% load when the water is not near ninety degrees, but it overheats and stops suddenly (with no sputter) right now in mid-summer at that load. It will run either unit all day long, not both, at closer to 50%. The manufacturer says that he has people in south Florida running Barnacle Buster through them 2-3 times a year to keep them cooling properly. Being a brand new genny with only 70 hours on it and run with freshwater cooling before every shutdown I pooh-poohed that idea. And then I did it anyway - holy cow was that water murky with scale!

rgano said:

Although I feel sure earlier suggestions will lead you to your solution, I have one more thing to say regarding summer heat. My little bitty 3.5 KW generator runs my 13.5 KBtu rooftop and my 10 KBtu marine ac units simultaneously at 80% load when the water is not near ninety degrees, but it overheats and stops suddenly (with no sputter) right now in mid-summer at that load. It will run either unit all day long, not both, at closer to 50%. The manufacturer says that he has people in south Florida running Barnacle Buster through them 2-3 times a year to keep them cooling properly. Being a brand new genny with only 70 hours on it and run with freshwater cooling before every shutdown I pooh-poohed that idea. And then I did it anyway - holy cow was that water murky with scale!

Click to expand...

That would be your temperature switch shutting you down. We suspected ours was doing the same thing after the Northern Lights factory tech support guy said there was a known issue with those switches. However, the generator started and ran for ten straight hours last Sunday with three a/c units, a refrigerator, an ice maker, and a wine cooler all running. No shutdown issues. We have a new switch but haven't had a chance to install it yet. Very strange situation.

But you're right about critter growth this time of year in Florida waters. Need to stay on top of it. A Barnacle Buster (or equivalent) flush twice a year, spring and fall, is part of our routine.

John

Last summer, my NL 5kw would start and run for a few minutes and shut down. It turned out to be a faulty auto shutdown switch for high temp. The genset is 12 years old, 1500 hours. NL said it was a rare problem but that it happens.

Based upon direct readings of the heat exchanger surface with my no-touch thermometer, I was actually overheating at 225F which is the shutdown setting of the thermal switch.

The switches on the NL genset are NO, they short to ground when activated. so to test one or the other, just disconnect it from the “grey wire” circuit and tie off the loose connector so it can’t touch the block.
If you do not believe an actual fault exists, then you can disconnect the oil pressure, coolant, and exhaust water temp switches and bypass them.
Most likely is oil pressure, and then coolant temp. If it shuts down with all three switches disconnected, then more likely a relay. They are cheap, replace them all. Next, the diodes between two of the relays. They are leads components like from a through hole circuit board, soldered together and then connected to the relays. Leads can break.
This is not a fuel issue. It is electrical. Everything stated here is a relay from various NL tech support. I would ignore well meaning suggestions that are not specific to NL gensets. Good luck. PM me if you like.