Northern Lights 12kW Generator Overheating


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Over the last few months the generator running temperature has been slowly increasing. We were still below the 205F cut-off level, and the generator continued to run fine, but something clearly wasn’t right.

The generator normally runs in the 192F to 193F range at full load and I have a warning set at 195 that sets a yellow light on the dash and send us email. The reason I set a warning indicator at such a low level rather than waiting for it to get up over 200F, is this allows me to catch most impeller failures early where I can just do a 30 minute impeller change rather than having to drain the antifreeze, take apart the heat exchanger, and dig the broken impeller parts out of the heat exchanger inlet.

If I wait until later, the generator will overheat and shut down during a run, potentially at an inconvenient time. And, more important, if you replace the impeller before the fins break free, you don’t have to take apart the heat exchanger hunting for impeller parts.

A couple of months back, the 195F warning fired. I’m used to this one and figured it would just be the usual quick impeller change. But the impellor looked fine.  The next mostly likely is a fault temperature sensor but, using an IR heat gun, I can “shoot” the head at the temp sensor and see if it’s reading accurately.  The sensor also tested fine. So, we had a slightly warmer than usual generator but we were also running in warmer water than we have seen for years on Lake Saimaa Finland where, even this early in the season, the lake water is already 61F. I figured it was likely the warmer than usual lake water. And, as soon as the generator is down below 100% load, it runs at normal temperature, so it wasn’t a big issue.

During the most recent generator run, the generator temps had crept up to 202F which is far too close to the 205F cut off used by Northern lights to shut the generator down. It was time to dig deeper and find the cause of the slowly-escalating generator operating temperature.


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The first thing I noticed is tiny spec of green antifreeze residue on the coolant circulation pump. I pushed on the spot and was a bit surprised to see coolant actually spraying out under pressure. The coolant circulation pump had corroded through. When I found the problem, it wasn’t yet leaking but the screwdriver pushed straight through the side of the pump when I pushed on it. The pump was paper thin and now the pump had a quarter-inch hole left by my screwdriver probe.

Clearly the first job was to change the coolant circulation pump. This is an easy job on a small Northern Light generator like our M843NW3.3. But since the coolant was full and there were no leaks prior to needing to change this pump, it almost certainly was not the cause of the higher-than-normal generator operating temperature.

To change the pump, I pop off the sound cabinet at the front and side, drain the coolant, loosen the water pump drive pulley, loosen the alternator, remove the drive belt, remove the water pump drive pulley, remove the coolant hose from the pump, remove the 6 fasteners that hold the water pump to the block, and remove the pump. I wire brushed the gasket surface until it was shiny and clean, replaced the gasket (I used a light coating of Permatex Red high temp RTV), and then re-attached the pump. Then I torqued up the pump, installed the pulley, belt, and tighten the alternator at the correct belt tension (roughly 1/4” deflection when pressed with finger).

Then I refilled the antifreeze and retested the generator at full load. Predictably, it still ran up over 200F.  There wasn’t much belt residue at the coolant pump or alternator pulleys so I knew the belt hadn’t been slipping. We now have a new coolant pump installed, so that wasn’t the problem either. The raw water pump impeller was fine, but I was concerned that the coolant may have become acidic since the pump should not corrode through.


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I checked the engine air filter and it was free-flowing and not a problem. The exhaust elbow was changed 1,500 hours back and I run fairly high load and don’t have carbon buildup in the exhaust so I didn’t bother to check it.

For the next phase, I drained the coolant back out to check the heat exchanger.  Here I’m checking the PH of the coolant using a handheld PH tester from Amazon. The coolant measured 9.1, which is slightly alkaline and just slightly lower than new coolant. From this test, the coolant appears fine but that’s not completely surprising since it was just changed 5 months back while we were in Amsterdam. Perhaps the old coolant was a problem or perhaps the coolant pump was just flawed.


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I next decided to check the thermostat since I was seeing slowly escalating temperatures and thermostats can fault in this way. This is an easy change where 4 bolts are removed from the side of the heat exchanger and the thermostat spring and thermostat come out. And the gasket surfaces need to be wire-brushed until shiny and clean before reassembly. I put a thin layer of Permatex RED high temp RTV on the gasket and then it all went back together quickly.

If you look closely at our thermostat in the second picture above, you can see that the thermostat is warped slightly and the movable inside section is scraping against the outside section. This can cause exactly the symptoms we were seeing, so I changed the thermostat, refilled the anti-freeze, and tested again at full load.

Unfortunately, the generator still ran on the hot side at full load, so the scraping thermostat wasn’t the primary issue and may not have been an issue at all. The generator was still hitting just barely above 200F at full load which allows it to operate without a thermal shut down but it’s far too close to the line.


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I drained the coolant for the third time and this time took apart the heat exchanger. I probably should have investigated this prior to changing the thermostat, but the thermostat is such a quick and easy check, I did it first even though it’s less likely to be the problem.

Removing the heat exchanger is easy. Remove the heat exchanger rubber boot at the front of the engine. Loosen the boot at the rear and push the heat exchanger bundle forward and then pull it from the front out of the housing. I found 8 or 9 heat exchanger tubes plugged, which is not a total surprise for a 5,600 nearly 10 year old generator. On our last boat, I used a gun barrel cleaner but I don’t appear to have it any more so I improvised and cleaned out the tubes using a short section of heavy gauge wire. When they were all nice and shiny and rinsed our clear, I reassembled the system, refilled the anti-freeze and tested.

The good news is that it was much better. The system now ran below 200F at full load so it was doing pretty well but I know it never ran that hot before, so something still wasn’t 100% right.

But, there was one concern from the first picture above. If you look closely a thin layer of perhaps 1/8” to 1/16” of residue is visible on the outside of the tubes.  The residue was thin, so I didn’t think it was a likely cause and didn’t go after it at this time (but I should have).


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At this point, I had investigated most reasonable causes of excess operating temp. I know the raw water pump only has 1,000 hours on it and the impeller is good but it’s an after-market  (non-Northern Lights pump) which I was encouraged to try and I sort of regret getting it. It’s a great pump and has operated flawlessly but I just feel better with the manufacture pump on there. If something weird happens and the shaft breaks, the engine gear train can be destroyed. This almost never happens, but I still would prefer to use the factory pump and I have one on hand so I decided to change the pump and keep the aftermarket pump as a spare since it’s only been lightly used.

The raw water pump is easy to change. Take off the top and bottom hoses, unscrew the top and bottom hose barbs to use on the new pump unless you are replacing them, remove the four fasteners, put an oil diaper under the pump, and remove the pump. The new pump went back on quickly. I refilled the anti-freeze and tested the gen at full load. It still ran right around 200F.

Northern Lights engine expert Bob Senter has mentioned many times that incompatible antifreezes can cause problems. Apparently the old John Deere coolant used in the past is incompatible with HOAT/OAT/NOAT type anti-freezes that are becoming common and the mixing of these antifreeze chemistries can cause rapid corrosion and over-temperature. Since this engine is showing some of both, I took Bob’s advice of flushing the coolant system.  The Nordhavn yard says they used Fleetguard ES Complete and I’ve used nothing but ES Complete blue label so there should have never been a coolant mix in the engine. But, I’ve checked just about everything else, so I would flush the cooling system and put in all new coolant as a next step.

To this I drained the coolant for the fifth time, put in water, ran the engine, drained it out (sixth time), and then refilled the coolant with 1 cup of dishwasher detergent (picture at top of this post) and the rest clear water.


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Click image for a larger view

I ran this mix of dishwater detergent and water for a couple of hours and the generator never got above 190F at full load. This is better than the engine has been for at least 5 years. I drained it out (7th time) and in the picture above you can see how dirty the water came out. I repeatedly drained the coolant, refilled with freshwater, and ran the engine until the water came out clean. Then I refilled the system with new coolant. This ran up the “drain the antifreeze” count to 12 :-). But the good news is it has run for several days now with the coolant temp never exceeding 192F.


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While working on the generator, I always have to be careful to have generator auto-start shut off. This last operation of flushing the antifreeze took some time and, while working on the generator, the control system detected the house batteries needed charging. Of course, since I have autostart off, it failed to start the generator.

What I thought was kind of cool is the batteries need to be charged, and since the control system was unable to start the generator, it failed over to emergency-backup generator (two generators when you only have one) which on Dirona is the main engine. The main engine automatically started up, the RPM climbed to charging RPM, and it ran until the batteries were charged.

This is exactly what it’s supposed to do. If the batteries need charging and the gen won’t start, can’t start, or stops running, the main is run to charge the batteries. It’s not a surprise to see it start, but it’s great to see everything just work as designed. In the picture above you can see the main engine is currently producing 7.6KW which is that far below what our 12KW generator charges at. The main is an excellent backup to the generator but, in fairness to the generator, the main engine has actually only been needed as backup once.


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I worked for a six years as an Italian car mechanic servicing Alfa Romeo, Lamborghini, Ferrari, Fiat, Lancia, etc. And, of course, I’ve seen my fair share of vexing cooling problems but this one has actually been more challenging than most. It’s now running exactly as it should, where after 20 minutes at full load the whole time in 61F lake water, the generator temperature is only at 188F.  It has lots of cooling margin at this point. In fact, I don’t think the 180F thermostat is even fully open until 190F. It’s looking perfect.

What I’m left wondering about is the root cause of this problem. I’ve never used any antifreeze other than Fleetguard ES Complete blue label. This is an excellent antifreeze and I wouldn’t expect to see any problems with it. The cooling system gets new antifreeze every two years, but even with good coolant and proper changes, it was a bit of a mess. The engine showed no signs of exhaust leaks into the coolant. It produced full power, there are no bubbles into the coolant, and all cylinders are running at the same temperature. I suspect that I have a coolant quality problem but, if that is the case, I should see it again I’m running a new load of the same brand coolant.

If there are any signs of coolant problems in the generator over the next 6 months or so, I’ll not trust the coolant I’m using and replace it in all three engines. It’s good to see the generator back to running like new but it ended up taking nearly a day to chase it all down.

Thanks to Bob Senter for recommending the dishwasher detergent flush. It ended up making the difference. The generator hasn’t been above 192F in over a week and we have been in water as warm as 69F.

 


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27 comments on “Northern Lights 12kW Generator Overheating
  1. Dave says:

    James,
    This is somewhat off-topic but I’ve wondered if you might have considered running your boat with a serial electric hybrid system. Three-phase AC marine electric motors from places like ELCO are efficient and very reliable. It seems to me that if you are typically running a hotel load along with the propulsive load, it might make more sense to run one or two three-phase gensets to generate motive power.
    The advantages I see would be:
    -quiet & efficient operation at the genset’s most efficient RPM
    -excess power could charge batteries
    -the wing engine could be replaced with a smaller electric motor for low-speed operation

    It’s a difficult solution to model, but I was curious if you considered it with Dirona.

    • Diesel electric is an attractive idea and that is how most cruise ships, train locomotives, mining trucks are driven. It has many advantages. It’s a great way to get extreamly high torque to each axle. A common cruise ship configuration is 3 V12 diesels and 3 V16s and these engines run the hotel loads, the thrusters, and the azipods. When more power is needed, they run more engines and when less is needed they run less. I’ve played around with the idea and like it but it’s not practical to install post-build. It’s also challenging to get the design right. Two larger Nordhavns where built diesel electric and the owners of both ended up giving up and the boats were returned to standard mechanical propulsion.

      In a smaller boat like ours, I don’t think I would be willing to give up the efficiency and reduced range of diesel electric even with all the advantages.

      • Dave says:

        Thanks for the reply!

        In fact I went on a behind-the-scenes tour of the Golden Princess once, and I saw on the electric management board the number of active diesels and the total load generated. She was able to move in the Gulf of Alaska at 20 knots while powering her hotel loads with only 4 of the 6 engines running.

        But that touches on the downside – there’s a substantial amount of mechanical fitting needed to modify a direct-diesel vessel. Also, those large cruise ships have a dedicated engineering team for optimizing the current mix of power generated and power delivered, while emulating that kind of expertise in some kind of energy management computer would be complex and probably full of weird corner cases.

        Diesel electric might make a little more sense in a sailing vessel, where the motors could also be used to generate electric power, and there is a good use case for low-speed energy efficient motoring to supplement wind power. It’s less clear that a motor vessel running flat out at top speed for hours would substantially benefit, unless there is a large continuous hotel load and/or the generators were substantially more energy efficient than a direct drive motor.

        • I think you are right. It’s harder to make diesel electric work well in a small boat where there is a hard limit on the amount of fuel that can be carried and, as a consequence, fuel efficiency matters greatly. And we don’t really have the massive load changes where diesel electric really shines.

          A related idea that interests me greatly is to replace a 12 to 16 kw generator with 2 6kw or smaller generators and bring the generators up and down as loads change with a battery/inverter absorbing the load during startup. I like the idea of more closely matching the load to the generator capacity.

          • Dave says:

            One way you could start in that direction would be to replace the 40 HP (30 kw peak) wing engine with the Elco EP-40 three-phase AC motor, along with a three Victron Quattro inverter/chargers operated as a three-phase system and maybe another diesel generator. Then any combination of available AC gensets and batteries (or even the main engine alternator) could power the wing motor. This would allow you to re-use some of the space used by the wing engine with a genset, and make the “get-home” motor even more reliable – supposedly 50,000 hours between required maintenance because there’s only one moving part. It would also allow reuse of genset capacity.
            I’m and electrical engineer, so I admit I like the idea of transforming problems into electrical problems. But it’s fun to think about, at any rate.

            • I’m a sucker for new engineering projects but, as much as I like your suggestion, getting these designs right takes time and investment. I would love to work with a company to engineering an excellent solution. But, doing the engineering for just a single boat doesn’t make sense. The project needs more scale to look good economically but I love the idea and would love to be involved with a project on the lines you describe.

  2. Bob Breen says:

    Great post, James. I recently attended Bob Senter’s two-day hands-on diesel class in Ballard and was able to follow all your troubleshooting steps thanks to Bob’s great instruction and your clear writing. Before Bob’s class, this would have all been pretty mystifying!

    I also read your post about storing your spare parts. With so many parts spread out across multiple areas of the boat and various boxes, do you have some kind of tracking system to help you find a part when you need it? I’ve got a slew of spares now, with more coming, and I’m worried I’ll lose track.

    Thanks again!

  3. Chris M says:

    Hi James and cheers from Seattle! Now that AWS Outposts are seeing some public light of day, I’m curious of you’ve had the urge to upgrade your power system to run one on the boat? It seems like that would be a pretty cool use case to bring the AWS Cloud everywhere!

    • It would be very cool but the boat is poorly connected by data center standards and has limited space and power so an Outpost won’t squeeze in. We would need a much bigger boat. But, we do run everything off of AWS. We have a central database where all on board telemetry and control information is stored. It’s fairly busy with well over 100 requests per second. From there, a subset of the data is uploaded to AWS where the mvdirona.com web site is hosted. The AWS account also provide access to the boat control systems when we are away from the boat.

      • Chris M says:

        That’s awesome that you have been able to integrate that much with AWS. You must have some unique and robust data queuing and transfer backoff solutions to handle the connectivity challenges where latency could be measured in days until you have a [cost-effective] link again. Have you thought about grabbing a Snowball Edge to get a smaller taste of EC2 on-board until you can talk them into building an Outpost Pi? I’d think that would be a good way to periodically sync the superset of data to AWS for long-term retention and trend analysis. Greengrass seems like a potential option as well.

        Of course, this all assumes you don’t want to spend time just enjoying your travel. ;-)

  4. Per-Ola Selander says:

    James, I assume the heat-exchanger insert is made of bronze. In the Volvo Penta manual, I was recommended to use Muriatic acid to clean the oil-cooler insert. Given it was much smaller, only about a hand long and could be submerged, it was an easy job. And engine was never “in danger” as the procedure was only part of a (for me) preventive maintenance I undertook as I took most of the engine apart one summer.

    And as always; amazed you have time to both maintain Dirona in bristol condition – AND keep your WW audience abreast with what is going on. When it comes to technology or to adventures – and when they happen to intersect. Planned or not.

  5. Greg Moore says:

    Hi James – very informative article! Have you considered using Barnacle Buster to flush cooling systems? I’ve done it a few times now on my mains and it really cleans out the salt water side of the cooling system. Plus, it really is easier than pulling apart the cooling bundles on my engines. I’ve been very impressed with the results-

    • I’ve heard good things about Barnacle Buster for cleaning the raw water side of the heat exchanger. Despite all the stories I have heard about plugged up sea water systems, we have never had any trouble with ours and, even 10 years later, it’s still bright and clean. This particular issues was the jacket water (coolant) side of the heat exchanger had built up an insulating scum layer over 10 years and just under 6,000 hours.

      Thanks for the Barnacle Buster recommendation.

  6. Paul Wood says:

    Hi James,

    I wonder if this could be a case of the “fouling factor,” especially so if this is the first time the heat exchanger has had a proper cleaning flush. The coating on the heat exchanger tubes gradually builds up over the years and becomes like a form of insulation on the heat transfer tubes. Thus causing overheating.

    As you’ll know, all good heat exchangers are over-engineered to cope with this fouling factor issue so that they operate within spec for quite some time until eventually, it becomes a shutdown scenario due to overheating.

    I used to spray wash division plates and tube bundle exchangers with an alkaline solution, followed by a thorough rinse, reassembled and put back into normal operating service.

    Totally unrelated, and is more of preventative medicine. Giving washing machines etc a service wash with a tub of Bicarbonate of Soda once every 3 months works wonders for cleaning scale of heating elements, pump impellors, thermostat bodies :)

    • The heat exchanger fouling was either what Paul is calling “normal fouling factor” or some form of anti-freeze contaminant. Paul’s suggestion is the most likely of the two.

      Your Bicarbonate of Soda flush for washing machines sounds like a good idea in hard water applications.

  7. Brent says:

    As an ex Italian car Mechanic you would be a master of problem solving. You are definitely next level with tech. One thing to consider is growth or barnacles inside your sea cocks for the raw water inlets to the heat exchanger.

    • We did think of that but it’s never been a problem over the 10 years we’ve owned the boat and, since the only way to solve that one is to dive the boat, I decided to check other things first. But you’re right it does happen. I’ve heard from many that have had that problem but, for some reason, we’ve never seen the raw water inlets plug up. Perhaps everything gets used too frequently for build-up to start?

  8. Kenneth Geller says:

    I have worked on hearts not generators, so I am not exactly familiar with what you did. However, your problem solving was great.

    • Thanks Kenneth. On this problem, I probably should have gone to the heat exchanger more quickly. I suspect that the antifreeze I was using may have a problem but we’ll know if this problem returned or it stays clear since the new antifreeze added is from the same batch

      The cooling system is now very clean so if any problems return, then the it’ll be an antifreeze problem or a some leak into the cooling system.

  9. marcus says:

    really informative post – thankyou

  10. Tim Gillingham MV Iriana says:

    I have been having the same overheating issue with on our 16kw NL. This is a great guide to working through the system.
    Thanks for the comprehensive post.

    • Good luck in working through your issues. Generally, the generators are well engineered with systems that are easy to access so it shouldn’t be hard. The heat exchanger is a popular place to find issue with bits of raw water impeller often plugging the forward end.

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