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Old 09-04-2022, 08:29 PM   #1
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Default Onan generator

Why does our onan generator surge all the time? Because of this, when you turn on the microwave or A/C, they make a terrible noise and the generator quits running.
Thanks!
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Old 09-05-2022, 01:47 PM   #2
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Surging is the choke not adjusted and when you put a load on the gen, it kills it. If you can, you need to inspect the gen carburetor and clean it up. This is a known problem with gens. You need to run the gen for 30 minuets at least every month with a load on it. Also, you need to add a soft start capacitor to the A/C to make it easier to start. A small engine shop may can work on your gen problem better than a costly RV shop.
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Old 09-05-2022, 03:33 PM   #3
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Thank you so much!
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Old 09-05-2022, 03:36 PM   #4
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Most of the time, based on what I have seen on others and on ours when we still had it, the surging is caused by a mostly plugged up carburetor in the very small gas internal passages. It happens worse and much faster if you have to use gas with ethanol added like we do in Minnesota.


As long as the engine will still run, albeit poorly, you do stand a pretty good chance of fixing it without removing, or even looking at, the generator itself.


Running the engine on new gas with a cleanout dose of Seafoam additive has fixed many Onans over the years, including ours.


1. I think the best way to do it is to use up as much of the existing gas in the van that you dare do if it is more than a couple weeks old.



2. Fill the near empty gas to about 1/2 full so you have enough to let the generator run.


3. Add enough Seafoam to the gas tank at the cleanout rate which is about double the storage rate. It will take quite a bit.


4. If the engine is prone to killing when a load is on it, don't do that for a while.


5. Start the Onan with no load and let it run 20 minutes with the gas and Seafoam going through it. There is no need to go longer than that.


6. Let the van and Onan sit 24 hours and repeat the 20 minute run. If it has smoothed out some, try putting a fairly small load on it and see how it does. If it carries the load and doesn't kill you know it is helping.


7. Let it sit 24 hours and repeat the above but after 5 minutes put on the small load and if it continues running add more and more load until it either starts surging horribly or dies. If it does run poorly at higher load, back off the load and let it run the rest of the twenty minutes at the reduced load.


8. Repeat number 7 as many time as it takes to get smooth running under load.


9. If it gets smooth at all but full load or sags in rpm when you put on the full load, you might be able to take care of that by removing the cover of Onan and setting the elevation knob on the carb to a lower elevation. This will richen the mixture and might be enough to take care of full load issues or a big sag in speed when the full load is added. Ours needed that change.



10. If the Seafoam fixes it, to prevent it from happening again you will need to add Seafoam to the tank any time it is going to sit anything more than about 3 weeks if you have ethanol fuel in the tank and Onan, but you can use the storage amount for that. When it is going to sit, add the Seafoam and then run Onan until at least completely warm. The generator should be run for at least 20 minutes once a month per Onan, and I think that is important if it sits outside where it might get moisture and condensation on the slip rings section of the generator which will corrode them. Our van sits inside in a heated shop when not in use so doesn't see the radical temp swings that it would outside in Minnesota, so we were able to run the Onan much less often. Whenever you run it after storing a while it is good to have Seafoam in the gas, but it can get expensive to do. Buying a gallon at a time can help on the cost many times.


Let us know if you try this and how well it worked, or not, for you as that is always interesting to know.
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Old 09-06-2022, 07:41 AM   #5
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Old 09-06-2022, 10:47 AM   #6
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If you're handy, you can disconnect the fuel line to the generator and place it into a container of Seafoam and gas. Seafoam recommends 1 part Seafoam to 2 parts gas. That's a lot of Seafoam if you intend to run the generator off your van's gas tank.

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Old 09-06-2022, 11:11 AM   #7
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If you're handy, you can disconnect the fuel line to the generator and place it into a container of Seafoam and gas. Seafoam recommends 1 part Seafoam to 2 parts gas. That's a lot of Seafoam if you intend to run the generator off your van's gas tank.


This will work, Seafoam says you can use up to 50% concentration even. The normal concentration for cleanout is 2oz per gallon (128oz), so one to 64 ratio. The major issue I have seen is getting the engine to start and run with high concentrations of Seafoam so if I need a cleanout and have access to the fuel line I just drain the carb bowl and inject a 50-50 mix of seafoam into the carb with a suction gun. Gravity feed will also work most of the time. Then just turn the engine over a few times and let it sit overnight or longer. When ready to try, drain the bowl and feed in some clean gas with bowl open to let the first flush out. Then close the drain and feed in clean gas, hook everything up and let it sit a bit to clear any flooding the probably occurred. Then try to start, using ether if needed.


Once you get to the carb if is often easier to just remove it and soak it though, but sometimes you can get to the fuel line and drain much easier.
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Old 09-06-2022, 02:30 PM   #8
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Thanks so much for your reply. We're not handy by any means and the generator is tucked way in behind the driver's side axle. We almost would need to put it on a lift for someone to access everything. We did put SeaFoam in the gas tank and have been running it off and on, but still doesn't smooth out. May have to take it to Cummin's.
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Old 09-06-2022, 02:52 PM   #9
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Thanks so much for your reply. We're not handy by any means and the generator is tucked way in behind the driver's side axle. We almost would need to put it on a lift for someone to access everything. We did put SeaFoam in the gas tank and have been running it off and on, but still doesn't smooth out. May have to take it to Cummin's.

What concentration (ounces per gallon of gas in the tank) did you use. If you are low on the concentration it will take a lot longer to work or may not work at all compared to stronger concentrations? A minimum of 2oz per gallon is needed, so if you have 16 gallons of gas in the van you would need a full quart of Seafoam which is two of the 16oz cans.
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Old 09-06-2022, 03:00 PM   #10
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Unfortunately, the gas tank was about 3/4 full when we added one bottle of sea foam. We're going on another RV trip in a couple of weeks, then will add another bottle once the tank fits lower, say 1/2 full or less?
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Old 09-06-2022, 04:21 PM   #11
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Unfortunately, the gas tank was about 3/4 full when we added one bottle of sea foam. We're going on another RV trip in a couple of weeks, then will add another bottle once the tank fits lower, say 1/2 full or less?

The Chevies have a 31 gallon fuel tank so half is 15.5 gallons. That is going to take a MINIMUM of a quart of Seafoam to treat properly. Don't go cheap on the Seafoam or the cost will just be wasted because it won't be concentrated enough to help.


Try to find Seafoam by the gallon in automotive parts store, farm stores, small engine and lawn equipment places, etc. Here in Minnesota I found gallons at Fleet Farm stores. If you own an Onan, even once you get it fixed, you will need plenty of Seafoam to keep it working so you need to budget that just like buying gas or changing oil.
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Old 09-06-2022, 05:27 PM   #12
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Ok, thanks for helping out. I'll take your word for it. Much appreciated!
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Old 09-11-2022, 07:13 PM   #13
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I went to a marine store and bought a 3-way brass valve that is commonly used in boats to enable pulling fuel out of multiple tanks. I ran the fuel line from the Chevy gas tank to this valve. One exit port hose goes to the generator. The other exit port has a barbed fitting installed. In our C210P Roadtrek, the 3-way valve is mounted on the front side wall in the back of the city water/shower drawer, with the barbed fitting pointing outward. When I exercise the generator a short piece of gasoline hose is put on the barbed fitting and the other end put into a small gas can, filled with 100% gasoline and laced with seafoam. Turn the valve to the gas can port and start the generator. This is also done immediately after any trip whe the generator has been run from the ethanol gas in the Chevy tank.
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Old 09-12-2022, 03:08 PM   #14
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Thanks for all the good info. Unfortunately, what you did is out of our league. Maybe I could take you advice to a person who could do that, whoever that is. Thanks so much!
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Old 09-13-2022, 11:03 AM   #15
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All the answers related to fuel, but one of the main issues is low oil. Even a couple of ounces will make a difference when the generator kicks into high gear. The higher the RPMs the lower the oil gets causing the system to stutter as a safety. KISS
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Old 09-13-2022, 11:29 AM   #16
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All the answers related to fuel, but one of the main issues is low oil. Even a couple of ounces will make a difference when the generator kicks into high gear. The higher the RPMs the lower the oil gets causing the system to stutter as a safety. KISS

I think that would only happen on the newer inverter based Onans as the older ones by necessity have to run at a fixed speed to hold frequency in the the very tight range. High load will actually slow them down slightly even until the governor catches up to added load.


From what I have seen in fixed speed engines, the time they are most likely to quit from and low oil sensor tripping is right after startup in colder weather. The oil is thicker so it drains back from the upper parts of the engine more slowly, leaving less in the oil pan. The oil is also slightly less volume from the cold to start with, also. If they make it through the initial start, the oil warms up and drains back faster, and it expands some, so it less likely to have level sensor issues unless you then get it unlevel somehow.
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Old 09-13-2022, 02:23 PM   #17
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Thanks for all the information. Oil is full and clean.
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