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Old 06-16-2022, 10:39 AM   #1
Join Date: Jun 2016
Posts: 94
Onan 5500 Marquis Gold Overheating


Hoping I can get some help/advice with what I've been dealing with for some time now. We bought e 2002 Fleetwood Fiesta 34B a few years back, with a Workhorse Chassis. It has a Onan 5500 Gas Marquis Gold Generator. I keep the oil topped off, but not to much, as this has also caused issues. All maintenance is done regularly. Last year we dropped the generator, adjusted valves, replaced coils, new fan belt, and I did a new Onan fuel pump and filter l believe two years ago, I also did the elbow kit to replace the filter at the carb that are prone to leaking. The generator is on the driver side, right behind the front wheel, so the fuel pump is having to pull fuel from the gas tank all the way at the back of the coach, a long distance! What's happening is when its hot outside the generator seems to run fine until I put a load on it, as in the AC units, it will run for 15-30 minutes then shuts off. It only does this when its 90 plus degrees. I then can let it cool, and it will start up and do the same thing. It only does this when its hot outside. During cooler weather it's fine. I found a PDF online (45 pages) from Onan that discusses overheating with their various models, ,and that during this overheating the fuel gets to hot as well as the fuel pump, causing a vapor lock. In this PDF they show various shrouds and ducting they offer that get retrofitted to the bottom of the generator to aid in air flow. They mention in many cases the cooling intake ends up pulling the hot air from the cooling exit, which is now extremely hot air, and it just ends up recirculating hot air, versus pulling cooler air into the cooling intake. This coupled with the heat being radiated from the ground, be it asphalt, or concrete, or even dirt, makes me believe I am truly having an overheating issue. In short, just looking for some input/advice, or what others have done if having the same issue. I have sent Onan customer support an e-mail regarding this to see if they can recommend what cooling ducts/shields they suggest for my generator with considering where its located, but haven't heard back from them yet. I love this forum, this group has helped me figure stuff out more times than I can count!
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Old 06-16-2022, 06:40 PM   #2
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Because of the age of your rv.. the get the most out of IRV2.. you need to start at the back pages in gen section or workhorse section.. then read forward.. I believe I have seen reference here.. about similar problems.. .. if I recall right.. members seem to recommend cutting a hole in side of door to gen compartment and covering with vent cover can just screw to door.. like plastic luvered vent cover. You can find anywhere.. I recommend that you go into a/p store or online and get 6in fan that is 12v and mount it where it could push more air on gen.. or the biggest you can fit.. or multiple ones.. cheap and see if that helps..

Now on mine.. I plan to add.. eng oil cooler.. something you could have easily added when you had unit out.. oil cooler kits.. fit on eng oil filter and run houses to external cooler.. you can use your imagination and configure something that fits..

I also recommend you contact FLIGHT SYSTEMS GEN REPAIR .. com.. they will walk you through.. if you eng is not quitting but gen Justus stops producing volts .. it is most likely regulator has gotten old.. see you tube vids by FLIGHT SYSTEMS GEN REPAIR.. or onan voltage regulator repair.. bet caps in regulator have gotten bad.. when was last time you cleaned armature slip rings ?
Good luck and keep us posted
2000 southwind storm, workhorse custom chassis with 7.4l vortec
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Old 06-16-2022, 06:53 PM   #3
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Location: Morehead City NC
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NHTSA recall on the 5500 Onan. Yes, the intake and hot air exhaust are side by side and locating the generator behind the front wheel puts it right where the hot air from the engine and exhaust get sucked inside. Doesn’t look that hard to make.
This may help some
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Old 06-20-2022, 12:09 PM   #4
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Would this recall still apply to my older 2008 Coach? Or would I just be trying to source the ducting from Onan?
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Old 06-20-2022, 12:16 PM   #5
Join Date: Jun 2016
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Hi there donr103 - I had read about adding a louvered vent to the compartment door, so I do have that on my list. I'm guessing it will just help with removing the heat soak from around the generator. Regarding installing a fan - Not sure where I would locate one, you mention pushing air onto it it, but where is a good place to mount so that it is pushing air to the proper spot on the generator?
We have only owned this RV for 3 years, so I'm not sure about the regulator or armature slip rings. Are these easily accessible to replace? Thanks!
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Old 06-20-2022, 02:38 PM   #6
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I would need pictures to hive you better opinions.. but one idea.. is.. if you cut in vent.. mount a 6in to direction most good ones are reversible.. so you try either direction for the air that works best.. many online places to shop.. I can only tell you.. from my experience.. look at spal and these are not cheap.. but they really move the air.. get idea which one or two you might like.. then hit favorite online store and grab some.. don't forget you will need relays and they got those.. anyway you can improve air flow.. yet keeping the water off of it..
So find the brushes and don't take them out.. see if you can see the slip rings.. if you can.. they can be cleaned with a slick stick.. see FLIGHT SYSTEMS GEN REPAIR on you tube.. by cleaning armature slip rings.. it helps prevent voltage regulator burn out..
Good luck and keep us posted
2000 southwind storm, workhorse custom chassis with 7.4l vortec
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heat, heating, onan, overheating

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