Northern Lights - overheating

[CapnCuervo]

I have a Northern Lights M773LW3 generator that has recently begun overheating after hours of use. It has about 3600 hours on it at this point.

The raw water is circulating strongly, and I recently had the sea pump and impeller replaced, so I don’t think they are the problem.

I have traced this down to the fact that it is running low on coolant after about 6 or 7 hours of use under load despite being full before that in the primary coolant fill and the expansion tank). To that point, as long as the coolant is full, it runs stead at about 180. That leads me to assume I should eliminate the thermostat as a possible issue.

So, I need to track down the source of this loss of coolant. I do not see any punctured hoses or cracked housings, nor can I find a pool of coolant anywhere that is seeping out.

Any suggestions for most likely culprits or places to start?

Thank you!

[GordMay]

In addition to a faulty thermostat, there are a number of other conditions, that can cause generator overheating:
1. Low coolant levels which could mean the coolant is leaking internally or externally. Leaking coolant could be a result of loose clamps or leaking gasket among other reasons.
2. Poor circulation of the coolant which could be caused by a collapsed soft hose leading to a restriction.
3. The diesel engine generator has accumulated dirt on its exterior. Heavy accumulation of grease and dirt on the surface of the generator hinders normal heat dissipation.
4. Over fueling the generator.
5. A broken cooling fan or improper fan belt tension.
6. Clogged diesel injectors. If the fuel injector is clogged, the system will have to overwork to compensate for the clogged injector which leads to overheating.
7. Clogged air filters can cause the generator to overheat and cut out.
8. Damaged exhaust that restricts exhausting.
9. Generator overload.
10. Low oil levels.

It is important to mention that a faulty gauge can lead to overheating, because if the generator is overheating, but the gauge is faulty, it will not trigger the cooling system, when the generator needs it. A faulty gauge could also indicate that the generator is overheating, when it is actually within its normal operating temperature. Ensure you double check the gauge.

“Replacing Thermostat in Northern Lights Generator”
➥ https://forums.sailboatowners.com/th...erator.161890/

TOP 10 GENERATOR MAINTENANCE TIPS & TRICKS ~ Northern Lights
➥ https://www.northern-lights.com/news...r-tips-tracks/

[tkeithlu]

While Gord has supplied you a broad review of generator cooling problems, the loss of coolant into the raw water is the likely culprit. The place the two come together is the heat exchanger. Dollars to doughnuts you have a leak therein, and best hope so, because the other ways of doing it include cracked blocks and similar disasters. If you can pressurize the coolant circuit while the heat exchanger is disconnected from the raw water circuit you ought to be able to see whether coolant is leaking into it.

[Manateeman]

The Green Frog is spot on as always. Heat exchanger ...high probability. Not a big job to pull out the core. Did you switch to a stainless exhaust mixer? Are you using a water / gas separator ?
Check every rubber part especially if you have a noise enclosure.
Great gen set so probably an easy (not head gasket) fix.
Manatee crew.

[Stewie12]

I would go with the heat exchanger too. Pull it out and examine it. As a quick fix I once soldered up the parts that had corroded away, probably due to a worn away engine anode. Never gave me any more problems.

[Library70]

Just curious, how does a guage "trigger the cooling system when the generator needs it"?

[GordMay]

Originally Posted by Library70

Just curious, how does a guage "trigger the cooling system when the generator needs it"?

Good question. IDK, but page 24 [26 0f 40], of a typical manual [Troubleshooting]:
➥ https://www.northern-lights.com/wp-c.../ONL843NW4.pdf

[Jetx]

The M773 may not be the same, but on my M673 there is a rubber boot on each end of the heat exchanger. Each boot has two hose clamps… a larger one that holds the boot onto the HX body, and a smaller one that clamps down on the protruding end of the HX core. If the smaller clamp is loose, or if the boot isn’t positioned correctly, you can lose coolant into the raw water and/or get seawater into the coolant circuit. I’d check those boots and clamps carefully.

[CapnCuervo]

This is great info. Thank you all. I did replace the mixing elbow with a stainless one about a year ago. I will pull the heat exchanger and examine as a next step. I estimate I’m losing about 1 cup coolant / hour.

[CapnCuervo]

OK. Here is the update. While pulling the heat exchanger, I noticed that the smaller hose clamp on the end cap on the intake side of the heat exchanger was completely loose. I had my genset serviced in Port Everglades, Ft. Lauderdale by the authorized Northern Lights dealer. Apparently someone forgot to tighten something when they were finishing up.

I inspected the heat exchanger while I was at it, and it looked fine. Then I reinstalled, properly tightened everything, refilled the tank, and ran her for hours. She did not lose a drop of coolant. Now, I’m spiking the ball and doing my end zone dance.

Thank you one and all for your help and suggestions. Jetx wins the day. Your assessment was spot-on.

[Jetx]

Thanks for reporting back, and glad you found the problem. One more thought, since that loose clamp was the culprit and there was evidently communication between the fresh and raw water circuits, you could have some seawater contamination in your remaining coolant. It might be prudent to drain/flush the coolant side a couple of times with fresh water, and then refill with new coolant just to make sure you don’t have any internal corrosion issues down the road.

[CapnCuervo]

Ha - good call! That was this morning’s project. I really am relieved to have the genset back up and running.

Thanks again!

[IRENE]

You are probably aware of this, but the smaller clamps should be tightened prior to the larger clamps on your specific NL.

Great work on the diagnosis and repair!

Jeff

[CapnCuervo]

I don’t think I was aware of that order of operations, but I did it that way anyway. Luck counts for something!