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Old 07-06-2018, 06:05 AM   #1
howes1387
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Default Onan 5500 generator question

For some reason when it is really hot out my generator will quit. Happens more so when driving down the road with it running. Yesterday it ran great all day shut it down at night and it wouldn't start again. It starts and runs for a minute then shuts down. Anyone have experience with that problem? I thought it may be a weak fuel pump but am not sure now, but it definatly seems fuel related.
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Old 07-06-2018, 10:01 AM   #2
1matcoman
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Default Re: Onan 5500 generator question

I have occasionally experienced the same type issue with the Onan's on my work trucks. You're right that it sounds fuel related. The first thing that I would check is to make sure that you don't have a rubber fuel line that may have a slight crack in it which will allow air to be sucked into the system.
Check that out first.
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Old 07-07-2018, 05:15 PM   #3
voltdr
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Default Re: Onan 5500 generator question

Had a similar issue with my Onan 7000. after checking many things, it turned out to be the fuel pump. After replacing it, I put an ohm meter on the old one, while applying heat via a heat gun, I could see the resistance increase with more heat.
Dan
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Old 07-08-2018, 04:53 AM   #4
Rich Biebel
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Default Re: Onan 5500 generator question

I could write a book on Onan random, intermittent shutdowns.

Heat is a big issue on air cooled gas burning units.

Installations in MH's and trailers often disregard the guidelines for proper cooling and isolating the cooler intake air from hot exhaust air.

Any machine install can be easily checked with a heat gun to see what the air temp is going in vs ambient air temp.

If warmer exhaust air is going in the machine it will run much hotter and can and will do serious engine damage..

Do anything you can to wall off the exhaust side hot air on the right side from being drawn in at the cool air intake. You can easily feel where that air is being drawn in under the machines left side front......

New style 5.5 and 7kw Onan generators routinely are installed in a way that the hot exhaust air can easily be drawn in on the cool air intake side.

It can cause fuel to vapor lock and the machine shuts down in extreme heat.

Contol boards and fuel pumps routinely shut down the machines in the same way and it is very difficult to diagnose since it is random.

I work on these machines all the time and since many are used commercially I routinely change both items.

Its a very common problem and unfortunately costly to repair mostly because the control boards are expensive.

I just had a machine mounted in a gooseneck trailer up front. Replaced control board and fuel pump and made some sheet metal to block hot air from being drawn in.....

This summer I have seen this problem develop in a brand new living quarters trailer. 20 hours on the machine.

Nothing stopping the hot air problem.....and the machine shut down just from the heat. A fan blowing the hot air away from the inlet side and it stayed running.

At that same event I replaced a control board and a fuel pump on a 5.5 that was shutting down after 15 minutes to a half hour of run time......
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Last edited by Rich Biebel; 07-08-2018 at 05:04 AM.
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Old 07-09-2018, 08:11 PM   #5
howes1387
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Default Re: Onan 5500 generator question

Thank you very much for the help and ideas everyone.
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Old 07-11-2018, 03:28 PM   #6
1752supgas
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Default Re: Onan 5500 generator question

My Onan 4000 with 67 hours was giving me fits , ran perfect for 10-13 minutes and shut down , would not restart until it cooled down . Rich recomended changing board and fuel pump , has been perfect since . Dont care which on it was so long as its fixed , 1 hour of my time repairing . Rich knows his stuff . Thanks again Rich and Matt
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Old 07-12-2018, 07:29 AM   #7
Rich Biebel
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Default Re: Onan 5500 generator question

Thanks....

Here's another scenario I just spoke to someone about...

Nearly new Motorhome and Onan 5.5 gas generator.

Unit shuts off if run going down the road but runs fine parked.

Owner says Motorhome engine exhaust is close enough to generators fresh air intake to possibly be the cause......

I also had one in the past that had the generators fuel supply tapped into the MH's fuel lines for the engine.

Parked with MH not running generator ran fine....

Drive MH with generator running and fuel pours out carburetor in a few minutes....

Also had a diesel with supply lines reversed.......Generator would only run with a full tank in the van.

How about one with an exhaust pipe gasket made by installer but had no hole for exhaust flow. Would not start.....


I don't make this stuff up......LOL
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Old 07-13-2018, 11:22 AM   #8
voltdr
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Default Re: Onan 5500 generator question

Rich,
You have helped me on my Onan issues in the past and I thank you. I also thank you for the stories too...........................
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