Generator overheating

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Henry J Fate

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I do not believe there is a "general temp code either. The genset could be shutting down due to temperature affecting another component of the system or what's even more likely, the microquiet needs to be serviced.

The fault code is the biggest clue when identifying a problem like this. Read the manual carefully to retrieve the fault code.
 

Isaac-1

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My guess is installation issue, either hot air recirculating (doubtful if it happens going down the road unless hot air from the engine is being fed into the cooling air inlet for the generator. Or possibly vapor lock caused by the generator fuel line being ran too close to the exhaust pipe, etc.
 

jrm1776

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Wife told me this morning that some piece was lost on her way down to Florida when I was stationed in the middle east. It was replaced but we're now sure that it's a oil problem with the genny. If this was working properly, we'd most likely be running the generator with no problems. Also research last tells me that no rigs out there run the overhead housing A/C units without the genny running. Kind of a bummer because if you have passengers and generator problems, they are screwed. Our dash was working overtime, but we're going to take it to cummins sometime soon and get them to repair the problem instead of messing with it myself. Think I'd rather it be fixed then replaced, these generators aren't cheap :)
 

jrm1776

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My guess is installation issue, either hot air recirculating (doubtful if it happens going down the road unless hot air from the engine is being fed into the cooling air inlet for the generator. Or possibly vapor lock caused by the generator fuel line being ran too close to the exhaust pipe, etc.
It was happening while going down the road. That was my thought to and wondering why the genny isn't getting enough air flow from the outside but then again, it's close to the ground and it's hot outside so it's just getting hot air with the breeze. It's gotta be a oil problem because of it spitting out oil. We thought we got that all fixed but something aint right still. We'll get it fixed this year though.
 

Old_Crow

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My generator was smoking and using oil for a long time. Then one day it quit making electricity, even though it ran fine. After taking it to a service center and finding out the repair of both the no electric issue and the smoking/oil burning would approach the cost of a new unit, I bought a low hour replacement from an RV salvage yard in Phoenix. Got a 7.5kw Onan with less than 150 hours installed for $2800.
 

Isaac-1

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On the oil spitting issue, is is possible that it was over filled? These Onan KY 4000's are sensitive to being even slightly over filled with oil. Check the oil level on the yellow dip stick and make sure it is not over the top of the range.
 

Gary RV_Wizard

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First learn to display the generator fault codes. The last one generated is probably still stored and available. That would give you insight as to why it shut down (but some of the codes are a bit vague, e.g. code 36). As I recall, there is no code specifically for overheating on an air-cooled generator.

An air-cooled genset like the QG4000 is highly dependent on air flow, usually from the underside. Something as simple as a plastic bag sucked up underneath can reduce flow enough to overheat. It could also be an electronic failure, where a circuit board expands in the increased hit and eventually causes a fault of some sort.

Also get and read the Onan Generator Handbook. It has lots of wisdom on the care & feeding of Onan generators, all in one place.
 

jrm1776

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My generator was smoking and using oil for a long time. Then one day it quit making electricity, even though it ran fine. After taking it to a service center and finding out the repair of both the no electric issue and the smoking/oil burning would approach the cost of a new unit, I bought a low hour replacement from an RV salvage yard in Phoenix. Got a 7.5kw Onan with less than 150 hours installed for $2800.
That's good to know, just in case I need to replace, thank you
 

jrm1776

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First learn to display the generator fault codes. The last one generated is probably still stored and available. That would give you insight as to why it shut down (but some of the codes are a bit vague, e.g. code 36). As I recall, there is no code specifically for overheating on an air-cooled generator.

An air-cooled genset like the QG4000 is highly dependent on air flow, usually from the underside. Something as simple as a plastic bag sucked up underneath can reduce flow enough to overheat. It could also be an electronic failure, where a circuit board expands in the increased hit and eventually causes a fault of some sort.

Also get and read the Onan Generator Handbook. It has lots of wisdom on the care & feeding of Onan generators, all in one place.
Wife found out Onan manual and going to go through it this weekend. Thought we knew a lot about this but fortunately learning quite a bit from this community, much appreciated!
 

jrm1776

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On the oil spitting issue, is is possible that it was over filled? These Onan KY 4000's are sensitive to being even slightly over filled with oil. Check the oil level on the yellow dip stick and make sure it is not over the top of the range.
We did see this as a possible issue and the yellow dipstick sits sideways, so we weren't sure if it was giving a proper reading but we ended up sucking some out when we also replaced some parts on it. I can't remember off hand which parts but I believe it was gaskets. I'll have to go over this stuff this weekend with the manual. Thanks for your ideas.
 

jrm1776

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Follow up with this and howdy folks. Long time no see.

I'm going to have a professional get this generator fixed up pristine working condition. Either with Cummins in Chattanooga or what's you all's thoughts on small engine repair shops? Think I should speak with them too and see if they're not outrageously expensive?
 

Isaac-1

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Don't take it to a typical small engine shop, carburetors and governors on generators require specific tuning which differs from most other small engine applications.
 

jrm1776

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Don't take it to a typical small engine shop, carburetors and governors on generators require specific tuning which differs from most other small engine applications.
Awesome, thanks Issac, I'll just bite the bullet and have Cummins look this over and get it back to spiffy working order.
 

Pgh_AL

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I've been throwing parts at my Emerald 1 for almost a month now to no avail. It runs as long as you hold the start button. It was running fine and just suddenly quit .

I've replaced the oil pressure switch , the fuel pump, spark plugs , changed oil & filter, replaced brushes , cleaned slip rings . However i did find a broken corroded connector wire on the brush .

I thought I had it there replaced connector no go . Im down to the control board . If that doesn't do it i dunno . The slip rings were black badly tarnished used scotch pad and fine grit sand paper .

Any one with any fresh ideas ? Thanks in advance
 

Henry J Fate

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Probably the control board or a connector associated with the control board. Most of those parts you threw at it could not cause the problem described.

Do you have good voltage and frequency when the generator is running?
 

Pgh_AL

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Probably the control board or a connector associated with the control board. Most of those parts you threw at it could not cause the problem described.

Do you have good voltage and frequency when the generator is running?
I don't know . How do you check that ? I didn't mind throwing all those parts at it . It might ward off future problems . Sorta PM if you will . If this control board does the trick it should be trouble free for awhile
 

Henry J Fate

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Cummins may have an analyzer for a control board or they may just swap it out with a known good one to see if the problem goes away.

Unfortunately we don't have either of those luxuries but it seems like it probably is the board. One thing that you probably should do (if you have not yet) is to disconnect all auxiliary controls from generator so that you only have the switch on the generator wired to the control board. That will really boil things down to the board. It may be that all auxillery controls are using a dedicated connector type cable so that you could disconnect it at the generator and eliminate the auxiliary controls and the cables that service them. If it all comes down to a new board, let's hope it works as they cost some cash.

You could call your nearest Cummins/Onan service center and ask them how they confirm a bad control board and if they could check yours.
 
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skydivemark

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Central Florida
My thoughts are vaporlock, I've been told by cummins/Onan tech rep that the 4ky is good at running in hot temps. I had a similar issue so I added a second fuel pump back near the fuel tank - problem solved.
 

Matt_C

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SE - Mich
JRM,
My "vintage" coach has about the same size generator, it is just 40+ years older. It will run the roof A/C, the microwave and the electric part of the water heater all at the same time.....
I suggest that you may have both of two problems:
First (is one I have seen and fixed) is that the fuel system is screwed up and it is routed where it gets too hot so the fuel is vapor locking and that is shutting down your power. Where the fuel line is close to something hot, wrap it with aluminum foil.
Second and also seen but I didn't fix it, was a generator installed wrong so the cooling airflow was not clear and wide open. The owner fixed this with a sawall and never had a problem again.
Good Luck
Matt
 

A Traveler

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Aug 25, 2014
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346
Because of the amount of power (watts) the AC draws, it will only run on shore power or from the generator. It is not possible to run it from the engine alternator/battery/inverter power source.
 
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