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Onan 5500 Stops After 15 Minutes - Momentum 351M

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  • Onan 5500 Stops After 15 Minutes - Momentum 351M

    I have a 2018 Momentum 351M and I am having a few issues with it, one of which is the Onan 5500 generator shuts off about 15 minutes after being started cold. Once it is warmed up, it only runs for a few minutes. I had a mobile RV repair place look at it and they replaced the fuel pump, but that wasn't the problem. I believe it is giving an oil pressure error code. The dip stick showed halfway between low and full, but I added oil during troubleshooting and brought it up to about 3/4 between low and full. It only has 30 hours and I have only put about 10 hours on it since I purchased it new, so it has the same oil from purchase. The issue started after sitting stored for a few months.

    Has anyone experienced a similar issue or know what may be causing the issue and how to fix it?
    Last edited by Robbrown2; 02-25-2020, 08:03 AM.

  • #2
    Originally posted by Robbrown2 View Post
    I have a 2018 Momentum 351M and I am having a few issues with it, one of which is the Onan 5500 generator shuts off about 15 minutes after being started cold. Once it is warmed up, it only runs for a few minutes. I had a mobile RV repair place look at it and they replaced the fuel pump, but that wasn't the problem. I believe it is giving an oil pressure error code. The dip stick showed halfway between low and full, but I added oil during troubleshooting and brought it up to about 3/4 between low and full. It only has 30 hours and I have only put about 10 hours on it since I purchased it new, so it has the same oil from purchase. The issue started after sitting stored for a few months.

    Has anyone experienced a similar issue or know what may be causing the issue and how to fix it?
    Does the Onan have a carburetor? If it does, sounds like fuel starvation due to jets being clogged once the choke starts to close (warms up). I had a Yamaha 1100 with dual carbs that I could remove, clean, and reinstall with my eyes closed I had to do it so often. Darn ethanol was a royal pain. On the motorcycle I learned to regularly run a product called "SeaFoam" in the tank that seemed to help. Once clogged, though, it took removal and (careful!) cleaning.

    If I'm right, once you get the carb fixed stick to ethanol-free gas ("marine gas").
    Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

    2017 Ford F-350 DRW, '19 315RLTSPlus

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    • #3
      Since you have own the RV approximately two years or more, have you exercise the generator as required in the owners manual? Onan generators must be exercise at least once a month. Exercising is done by running the generator for a full one hour under load once a month even during the months it is stored away.

      if you do not do this the carburetor will go bad on you. It cannot be rebuilt. Trust me as a person who has rebuilt many, many motorcycle carburetors and other small motors, for some reason the Onan carburetor does not seem to be able to be rebuilt. Asked me how I know this.

      I had to replace the carburetor on the generator in my previous toy hauler. I learn the lesson the hard way. Carburetors cost over $200. On my current Momentum toy hauler I have exercised it religiously since I bought it. I’ve never had an issue again. I do change the oil/filter and fuel filter every spring.
      2018 Momentum 376TH
      2016 RAM 3500 Duall
      y

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      • #4
        I haven’t ran it for an hour each month religiously, but I believe the longest it has been without being run was about three or four months.

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        • #5
          Bad or old fuel kills Onan generator carbs. This has been happening since the beginning of time. Try running some fuel additive through it and see if you can get the varnish out. If that doesn't work then you are looking at a carburetor.
          2017 310GK

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          • #6
            Originally posted by Robbrown2 View Post
            I haven’t ran it for an hour each month religiously, but I believe the longest it has been without being run was about three or four months.
            This is where the problem starts. Three or four months could very well be the problem.

            Disclaimer: There is no way for me to determine if you need a new carburetor or not. When fuel (especially ethanol fuel) sits in a float bowl, carb jet (very small passage), and any internal part of a carburetor it becomes gummy and takes on a caramel color. This will literally clog up the carburetor. I have found that using "Seafoam" (easily purchased at any Wal*Mart) on all my toys, (two motorcycles, commercial lawnmower, snow blower, weed trimmer, chain saw, you get the picture) works well and is a very good product that has been around for years. It works well keeping carburetor motors running clean when used as a preventative measure. EX: Anytime I store something for the season I add it to the fuel tank. I also add when adding fuel for the first time of seasonal use.

            Fuel that sits over time (usually a month) will start to gum up. It will also loose some of its octane. This is one of the reasons Cummins/Onan states to "exercise" the generator monthly. I do mine every three weeks on a Monday morning. I have a repeated reminder on desktop/phone/tablet to remind me to do this. It become second nature after time. If it is RV season and you are using the generator regularly, excecising is not needed. However, when in storage is is a must with Onan generators.

            Hope you don't need a new carburetor. But I'm sorry to say that what is happening to you happen to me on my last toy hauler with the exact same Onan 5500. I tried rebuilding the carb with my many years of experiance at rebuilding carbs. That carb was only the second one in my lifetime that I couldn't get running again. It hurt my pride, but I ended up spilling out $200 plus on a new one. However, it was an easy install (for me).

            Check you manual again about exercising and do reserch on Onan and I believe you will see that you are not the first or the last......Good Luck
            Last edited by vonzoog; 02-25-2020, 10:14 AM.
            2018 Momentum 376TH
            2016 RAM 3500 Duall
            y

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            • #7
              Try a very simple fix first. Onan's dipsticks are WRONG. If you fill the oil to to the top line it will shut down after the oil heats up. Something to do with oil expansion as it heats and then it hits to the too high sensor. Take it down to only 1/4 of the way up the hashmarks. Yeah, I know, you're saying, "Yeah right." Trust me I thought the same thing. It has fixed every person's issue with that. Try it, you like.
              Curtis, Christine, Cole, and Charlotte
              2007 Chevrolet Silverado Duramax LBZ, CCLB
              2020 Momentum 351M
              2004 Essex Vortex

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              • #8
                Very hard to diagnose remotely but 15 minutes is a long time to run a carb dry. How far from the generator is the fuel filter? Ignition issues will also mimic this as a bad coil or ignition component heats up and results in a stall. The OP stated there may be a code? Is there a flashing light that would indicate a code or issue? If you feel you have an oil pressure error, it would not be good to try and run it until a mechanical pressure gage was installed to physically check that oil pressure is present and meets specs. This should be ruled out first.

                A quick search resulted in some additional information below where the 15 minute description was an interesting find.

                https://www.rv.net/forum/index.cfm/f...print/true.cfm

                Curtis also raises a good point where something to add that some will miss is that the oil level is checked from the dipstick being screwed all the way in after first being wiped off clean.

                Jim
                Last edited by Guest; 02-25-2020, 07:45 PM.

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                • #9
                  Originally posted by Robbrown2 View Post
                  I have a 2018 Momentum 351M and I am having a few issues with it, one of which is the Onan 5500 generator shuts off about 15 minutes after being started cold. Once it is warmed up, it only runs for a few minutes. I had a mobile RV repair place look at it and they replaced the fuel pump, but that wasn't the problem. I believe it is giving an oil pressure error code. The dip stick showed halfway between low and full, but I added oil during troubleshooting and brought it up to about 3/4 between low and full. It only has 30 hours and I have only put about 10 hours on it since I purchased it new, so it has the same oil from purchase. The issue started after sitting stored for a few months.

                  Has anyone experienced a similar issue or know what may be causing the issue and how to fix it?
                  Robbrown2,

                  Did you find the issue with your generator?

                  Jim

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                  • #10
                    Had the exact same issue with my Onan 5500. Believe it or not, taking out a couple of cups of oil from the crankcase solved the issue. The problem is that when the oil heats up it expands and trips the overfill sensor on the engine (very sensitive). Only fill the oil to the very bottom of the "normal range" and you won't have any more shutdown issues.

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                    • #11
                      We had the same issue with our Onan 5500, Momentum 349M. Brand new. Dealer said it wasn't GD issue, take it to Cummins Onan. Cummins Onan said not their problem. Fuel starvation was the issue. We ended up adding an additional fuel pump at the tank. Used a factory Onan part. $128, plus wiring. Installed myself. Problem solved!

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                      • #12
                        In years past had same issue with an Onan in a class "A". I will second the comments about high oil level and what I noticed was with dipstick in it read full dip stick not screwed in shows right at add line a little low on the stick not inserted and no more issue. We did notice at certain angles it would still trip the high level sensor. I also agree with the use of Seafoam in the fuel during low use periods and end of season. A friend with a land scape company turned me onto it years ago and it works, it will some times remove varnish build up but is best as preventive.

                        Dave
                        flyfshrockies, 2021 imagine 2600RB, Ford F-150, XLT supper crew 3.5 eco boost with max tow. Dave and Toni (and the awesome Aussie Bayley, he's the social one)

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                        • #13
                          I just worked with another owner on the exact same issue. The generator would fire up just fine, run very well for 15 minutes and then shut off. If he waited a few minutes, it would start right back up. The carburetor was cleaned and adjusted. The oil was drained and replaced. But still, it shut down after 15 minutes.

                          The Solution? The onboard timer clock setting was incorrect. Even though it was the middle of the day, the timer thought it was "Quiet hours" and shut the generator down. I can't remember if he adjusted the "quiet hours" or if he reset the clock. But from then on, it ran perfectly.

                          EDIT - ADDITIONAL INFORMATION. I just talked to the owner. To resolve the issue, he went into the One Control settings and turned off the quiet hours. He said he believes this was on the screen where you set the generator to come on for low voltage. Please let me know if this resolves your issue and I'll bring it up to Lippert since this would now be the second generator with this issue.


                          Jim
                          Last edited by TucsonJim; 04-06-2021, 05:19 PM.
                          Jim and Ginnie
                          2024 Solitude 310GK
                          GDRV Technical Forum Moderator
                          GDRV Rally Support Coordinator

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