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Old 10-25-2022, 05:01 PM   #1
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Onan 2800 generator overheating

So my 2800 runs well and charges, but depending on load and outside temps it will shut down after running anywhere from 20 mins to an hour later.

For instance running the fridge, AC and temps around 70 and VERY humid it didn't last 20 minutes today. Sometimes if I'm just charging the battery and it's in the 30s outside it'll run for over an hour.

I did just service the unit (oil change, new spark plug, new filters, adjust altitude compensator) and no improvement.

I added in one quart of oil which it just over the mark on the dipstick. I then saw some evidence that overfilled onan units will shut down like mine. Does oil quantity have anything to do with overheating?

Where else can I start looking?

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Old 10-26-2022, 07:16 AM   #2
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Sounds like you have carburetor problem, but could also be a control board.

Has the unit sat up and not been exercised at any point in its life? Not unusual for carburetors to be gunned up and/or the float sticking to cause intermittent operation such as you describe.

How many hours on the unit?

Have you looked at the commutator and brushes?

It could also be a bad circuit board - Service Manuals for Onan’s can easily be found for free with a little diligent searching on the Net, and may quite possibly in the Files section of IRV2. You’ll need a voltmeter to make some voltage checks.

Service manuals for O
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Old 10-26-2022, 07:31 AM   #3
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Not suggesting that overheating is the cause of the shut down, but there are two reasons for the air-cooled generator to overheat:

Restricted air flow into the "cooling air intake" due to how/where it is installed in the RV.

Recirculation of hot air back into the "cooling air intake".
Brett Wolfe
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240
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Old 10-26-2022, 12:04 PM   #4
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What if the electric fuel pump is getting hot after running a while? As for the oil level, my 4000 says to check the level by screwing in the cap. If it’s overfilled it says it can shut off.
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Old 10-26-2022, 05:31 PM   #5
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Wonder if the foam insulation has migrated and has choked off vital cooling air flow.
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Old 10-26-2022, 10:04 PM   #6
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Gen sets suck up trash all the time.. some blows through.. some gets caught.. so use your cellphone with flash on and record all over it.. as best you can.. look for trash.. you might have to use a Jack to lower unit.. just enough to remove top cover.. use all safety precautions.. and motorcycles Jack is great.. if you got one or rent.. floor Jack and piece of plywood.. remove shields and blow air through all and each fin.. some members suggest that adding vents and small 12v fans is great.. I plan to add external oil cooler to mine.. not there yet.. also.. when things go haywire and don't make sense then keep critters in the back of your mind all the time.. critters love to eat the tiniest holes in fuel line that do not leak fuel.. but suck air.. they nest in worst places.. if your fuel line is over 10yrs.. you need to replace all of it.. even if it.. transition from metal to rubber over fuel tank.. good time to replace fuel pump and filter.. clean carb.. it is made to be cleaned in the field and 80% of time you don't need to take it apart.. read some of my past post as to how.. to clean arb on engine..
Good luck and keep us posted
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Old 10-27-2022, 11:34 AM   #7
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1800 hours so it's run quite a bit in its life, though I can't say if it sat for a while prior to me buying it or not.

I have a receipt for a new carburetor recently, while I can't vouch for it personally I'm kind of ignoring the carb for now.

Something is definitely overheating, guess I'll order in all the remaining parts listed above and plan on spending a weekend dropping the unit out.

Checked the oil again today and the level is perfect so that's not it either.

I do have the manuals for it as well.

Due to the giant pain involved with working on this unit, when I take it out I'm just going to fire the parts cannon at it and hope that takes care of the issue. I suppose it's also possible there's a mouse nest in the cooling fins or something too so I'll pull the cover and check that too.
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Old 10-27-2022, 11:39 AM   #8
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Check rv appliances section and many manuals are there.. also do manual search on line.. try Cummings website.. also.. if you plan to remove gen.. use all safety precautions.. no power.. unplugged.. no solar... pull all batteries negative wires off and wrap.. use cellphone with flash on and record.. to record each step.. label all connections and where they go..
Good luck and keep us posted
2000 southwind storm, workhorse custom chassis with 7.4l vortec
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Old 10-27-2022, 12:01 PM   #9
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Some folks have solved this issue on a gasoline unit by replacing the fuel pump, when fuel pressure is not up to spec the heat can cause a vapor lock and shut you down. This was true on carbureted automobiles also, BTDT.
Brian, 2011 Winnebago Via Class A on Sprinter Chassis
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Old 10-27-2022, 07:59 PM   #10
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For a Onan 4000

I used a piece of flexible 1/4 in plastic tubing (ice machine waterline) attached to my air blow gun to blow out the generator windings. I was amazed by the sand/pebbles/dirt dobber nests that I was able to blow out.

The shutdowns may have become less frequent afterwards but ultimately I eliminated the shutdowns entirely by replacing the fuel pump.

You can search and locate lots of instances where it is stated that high temps cause the fuel pump to stop and the generator dies due to lack of fuel. Of course the generator will again start when the fuel pump cools off and works again. Count me as one of those..

Good luck, you results may vary.
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generator, heat, heating, onan, overheating

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