Generator Overheating

[tpbrady]

I’ve been fighting this all summer and it is getting worse. It started off randomly running more often without overheating to now randomly overheating more often than running.

It a Northern Lights M673D. Here are all the things done over the summer:

A. New coolant expansion tank and heat exchanger core and rubber boots. The generator was used and sat for a couple of years. There was a lot of loose rust.
B. New thermostat.
C. New coolant pump and hose. The old passages for the temp sensor and temp switch were full of sludge.
D. New raw water impeller and stainless exhaust elbow. The old iron elbow was starting to rot out.
E. Flushed out numerous times with Prestone coolant flush and fresh water, but would never run with coolant flush longer than an hour without overheating. These flushes have always resulting in rusty colored water being drained.

I spent about 30 minutes with Northern Lights on the phone and their conclusion was the same as mine. Something in cooling passages in the engine block interrupts the flow of coolant as the genset heats up. The genset will Star warm up to about 170 on the temp gauge and then 10 minutes or so jump from 170 to more than 200 in 15 secs or less. If I didn’t catch it in time, the temp switch would shut the generator off.

One thing we both noted when flushing the system with water without running the generator, the passages immediately after the thermostat aren’t really flushed well as the water flows from the coolant tank through the hose through the water pump into the block below the thermostat. Since I have the thermostat out I am going to flush the system both statically without running the generator and then with a coolant flush. If I solve this I hope to have my generator cooling system training record signed off. If AI has a better suggestion, I am open to it.

Tom

 

[tiltrider1]

Have you ruled out a bad head gasket? I bring this up only because of all the things you have done have had no affect.

 

[Simi 60]

Rod out the heat exchanger?

 

[twistedtree]

Have you shot various locations with an IR gun to confirm that it’s actually over temp? A bad instrumentation ground is notorious for creating gauges that say disaster when there really is none.

It would also be interesting to shoot the inlet and outlet raw water temp at the heat exchanger. I’m not sure what the temp rise should be, but there should be one if the raw water is taking away heat. But too much indicates inadequate raw water flow.

 

[Retriever]

Is it really overheating, or just the gauge indicating high temp?

Is raw water flow normal? Any chance a hose is failing/delaminated and limiting raw water flow?

This is a pretty thorough look at overheating troubleshooting on NL gensets: https://mvdirona.com/2019/06/northern-lights-12kw-generator-overheating/

 

[tpbrady]

The heat exchanger core is new. I have used an IR thermometer and it is definitely overheating. As far as the head gasket is concerned, there is no steam in the exhaust nor contamination of the coolant. I am not ruling it out but there is nothing to indicate that is the problem. 590 hours on it.

Tom

 

[tpbrady]

To clarify on the IR thermometer readings, when it overheats, the coolant tank is 157 degrees, the coolant pump is 190, and the raw water output boot is 75. The temp sensors and switch are part of the coolant pump assembly.

Tom

 

[rslifkin]

What's the temp at the thermostat housing showing when it's overheating?

 

[tpbrady]

The thermostat is embedded between the coolant tank and the engine block. I removed it the other day and it overheated, just took a little longer.

Tom

 

[twistedtree]

To clarify on the IR thermometer readings, when it overheats, the coolant tank is 157 degrees, the coolant pump is 190, and the raw water output boot is 75. The temp sensors and switch are part of the coolant pump assembly.

Tom

That doesn't seem like it's actually overheating.


There is a 10mm bolt on the generator end below the junction box where all the ground wires come together, It's pretty common for that to work loose creating a poor ground, and gauges that deceive.

 

[STB]

I think there was an earlier post which said 200+ F in 19 minutes.

If it were me, I'd remove the thermostat and flush then heck out of it with something more powerful, maybe Evaporust Thermocure. The Prestone formula mat be a little less aggressive w.r.t. rust.

If you've got sludge, you know the problem, or at least one of them.

If that didn't do it, and I still was seeing sludge, I might try an acid solution. But, at a certain point, it may be worth pulling the head and seeing what those passages look like.

But, I suspect a good Evaporust Thermocure flush would do the trick you might need to run it over the course of a few cycles to get the job done given the overheating.

 

[tpbrady]

That temp reading was taken about 20 secs after shutting it down when the temp gauge read 200. The housing of the temp sensor read 187. The temp rises from 180 to 200 in the space of about 3 secs. Since that sensor is sampling coolant from the top of the block, the only plausible explanation is coolant has stopped flowing from the heat exchanger/expansion tank into the block. If I don’t catch the rapid rise from 180 to 200 the temp limit switch will shut down the generator about 10 secs later. That would mean two different sensors are giving false readings. I have a new sensor for the gauge coming next week. Short of any other suggestions I am going to run fresh water in the generator until it starts to overheat, shut down, drain it when cool, and repeat until the water comes out clean enough to drink. Hopefully it won’t overheat at that point. The longest I have run it was with water for an hour and five minutes before the temp ran away.

Thanks everyone for the suggestions.

Tom

 

[tpbrady]

STB,

I wish I could get hold of Thermocure, but being at the end of the road it’s about a 2 week delivery time from Amazon. Until it gets here I’ll have to go with what I can get locally.

Thanks.

Tom

 

[STB]

I would not run freshwater in the generator. With the heat, in an engine, it just promotes corrosion and won't really break it down at all.

Use a solution designed to solve this problem. My suggestion is Evaporust Thermocure.

Bad sludge problems can take patience

 

[tpbrady]

STB

Right now I am using Prestone Coolant flush since I can get it. It recommends after using it to run fresh water through it for 10 minutes then add coolant. I have 6 days of downtime to flush it until I run out of Prestone or water.

Tom

 

[BruceK]

The OP`s related history has me believing"it`s getting hot". Runs at normal temps for some time,suddenly goes off scale. Barring a temp signalling fault, intermittent but utterly consistently repeated,"it`s getting hot". Hope the flush fixes it, my Lehman with the usual no.6 silting issue took a number of flushing attempts with exotic cleaning potions until my mechanic exclaimed "I`ve got it!"

 

[STB]

STB

Right now I am using Prestone Coolant flush since I can get it. It recommends after using it to run fresh water through it for 10 minutes then add coolant. I have 6 days of downtime to flush it until I run out of Prestone or water.

Tom

I'd be cool running it with water and then draining it out to get the cleaning solution out. It would be a waste of good coolant to throw it away right away like that.

I just wouldn't want to run it that way a lot.

I'm with BruceK on this one: This is a problem that just takes persistence and is helped by the right flush solution.

The OP will get itnwith time and persistence, I suspect.

 

[jleonard]

Only thing I can add is to try a reverse flush also.

 

[High Wire]

Has the genny actually shutdown on temp or are you doing it based upon the gauge reading? Gauges do stick occasionally assuming old school electro-mechanical gauge.
The temperature shutdown set point is usually around 225F.

 

[Lepke]

Today's radiator/engine flushes are poor. The ones that worked well were made illegal about 30 years ago. Another thank you to the EPA.
Rust built up on the water side of the cylinder acts like insulation. So the coolant doesn't transfer heat as well. Also the head. You need to dissolve the rust using something like Evapo-rust. Rydlyme might be strong enough. Normally you mix it 1:1, but for this I'd use it straight. You can run the engine but only up to 180°. It works faster hot.

The rust forms because there was no anti rust additive in the coolant or the coolant was too old.

 

[C lectric]

There are two other acid type cleaners, Barnacle Buster and Rydlyme.

Both are best circulated through the cooling system. I just went through this with B.B. last fall. After sorting out the PVC fittings so I could circulate the cleaner from the 5 gal bucket through the system back to the bucket it did not take long for the water to go black. After a rinse I did it again.
I rigged a small bilge pump to pump into the engine and then the return line put it back to the bucket.

I used all PVC pipe and ftgs. since pvc is resistant, highly , to these acids.
Some clean vinyl hose, again resistant and inexpensive and I could see to get an idea what was happening.

I rigged the various outlets with ball valves to force circulation back to
the bucket through the various cooling passages as the wee pump 250 GPH, did not have the capacity to force feed the entire system at once.

My stat is a 180, in summer it was climbing to 190 or a bit over. NOw it does not move from 180.

So check to see if the other two are available more readily..


I have also loaded my tome which covers a lot of causes of overheating that
this may or may not cover.

Good luck with your endeavors.

 

[OldDan1943]

My NL had a problem. It would shut down after 10 mins. The tech came out, put a pressure cap….. pumped it up and discovered a leaking hose at a hose clamp. It was a ‘preformed’ hose…. He found ONE locally, installed it, we ran the gen for an hour and pronounced, cured.

 

[tpbrady]

I think I am over the hump. I have run the generator with the thermostat out for about 6 hours without overheating while running Prestone Coolant flush. The generator heated up to about 102 degrees verfied with an IR thermometer with 63 degree raw water. The water is still coming out brown so I plan to reinstall the thermostat and keep flushing. I'll have the Thermocure in about a week and will run that for about a week and drain and flush.

Tom

 

[rslifkin]

I wonder if the flush had dislodged some junk that was causing the thermostat to stick intermittently?

 

[sunchaser]

TP
I may have missed it before - Missing impeller parts in HXer or elsewhere?

 

[OldDan1943]

Thermostats are inexpensive, replace it.

 

[rncheney]

Just an observation. You make no mention of checking the thru hull or if you operate in a river or real silty water

 

[Simi 60]

There are two other acid type cleaners, Barnacle Buster and Rydlyme.

.

I've said it here before and will again

One is water based with a splash of phosphoric acid - so is salt water pool filter cleaner at considerably less cost or, I just buy phosphoric acid and add my own water and save again.

The other is water based with a splash of hydrochloric acid - 5 litres of Hydrochloric acid is $20 at hardware store here - water is free.

MSDS for rydlyme and BB are available online with % of active ingredient stated.