I browse this forum fairly often, but now I need some advice or expertise on what is wrong with my generator.It is a 6500 watt Onan. It starts up fairly quickly and generates power within a couple of minutes of running time, but it shuts down after about 5 minutes of run time with or without any load on it. It will restart after about a minute, but runs rough as it starts and then smooths out after about 5 seconds. It will then run for about 5 minutes before shutting down again. I suspect that it is not getting enough fuel, although it was serviced with oil change, new fuel and air filter about 6 months ago. All suggestions are welcome.

It sure sounds like a fuel system issue to me. Most like there is a very serious restriction in the low pressure side of the system. That could be anyplace between the tank's fill neck and the inlet to the fuel lift pump.The poor thing keeps trying to pump and draws a vacuum on the system up until it can't. Then, once shut down, fuel fills in the vacuum. I can't begin to tell you where to look except before the lift pump. Matt - 60yr a diesel engineer

hotjag1 wrote:I browse this forum fairly often, but now I need some advice or expertise on what is wrong with my generator.It is a 6500 watt Onan. It starts up fairly quickly and generates power within a couple of minutes of running time, but it shuts down after about 5 minutes of run time with or without any load on it. It will restart after about a minute, but runs rough as it starts and then smooths out after about 5 seconds. It will then run for about 5 minutes before shutting down again. I suspect that it is not getting enough fuel, although it was serviced with oil change, new fuel and air filter about 6 months ago. All suggestions are welcome.Gas or diesel?

Does it throw a code - flashing lights? It could be frequency or AC voltage problem. Model?

Reisender wrote:Gas or diesel?It says Onan Diesel Generator in the title of the post.

gbopp wrote:Reisender wrote:Gas or diesel?It says Onan Diesel Generator in the title of the post.Ugh. Doh. My apologies. So this is what I want you to do. Get your iPhone out and start your stop watch as soon as it starts. Then see if it quits at exactly 5 minutes. If so, I think I know what it is.

Onan diesel generator quits after a few minuthes

hotjag1
Explorer II
Feb 01, 2022
I did find the fuel filter on the frame rail and it looks clean on the outside so I don't know if it was changed or not. I will probably replace it tomorrow as that would be an easy fix if it is the problem.
kedanie
Explorer II
Feb 01, 2022
In those years, Tiffin added a second in line fuel filter that most would miss on maintenance. Follow the fuel line up and you should find it near the coach frame. You can remove it as it is not needed or find a replacement.

Keith
Reisender
Nomad
Jan 31, 2022
hotjag1 wrote:
Wow, I always thought I had a 6500w generator. Wolfe 10 was right. It is a 7500w gen. Model #5HDKAJ 11451H. s/n B030472922

I pushed on the top of the rocker switch which I always thought was for the glow plugs. If it is a primer switch, I didn't hear anything from the fuel pump when it was pushed. I am in 75 degree temps if that makes a difference.

The last time I got it to run, it ran for 3 minutes and 20 seconds. It is more difficult to start each time.

I have over a half tank of fuel according to the gauge which has always been accurate.

Hope I answered most questions.

Sorry I can’t help. If it didn’t shut down at the exact 5 minute point it’s not what I thought. (Faulty temperature sensor). Hope you find the problem.
hotjag1
Explorer II
Jan 31, 2022
Wow, I always thought I had a 6500w generator. Wolfe 10 was right. It is a 7500w gen. Model #5HDKAJ 11451H. s/n B030472922

I pushed on the top of the rocker switch which I always thought was for the glow plugs. If it is a primer switch, I didn't hear anything from the fuel pump when it was pushed. I am in 75 degree temps if that makes a difference.

The last time I got it to run, it ran for 3 minutes and 20 seconds. It is more difficult to start each time.

I have over a half tank of fuel according to the gauge which has always been accurate.

Hope I answered most questions.
bounder39zman
Explorer II
Jan 31, 2022
ONAN gen tech for 25 yrs here. PLEASE post full model/spec/ser no of gen so we know what we are working on ?
wolfe10
Explorer
Jan 31, 2022
Not familiar with an Onan diesel 6.5KW. 7.5KW, sure.

When this happens, before restarting, go out next to the generator and LISTEN while someone else pushes the prime button (if you have one). You are listening to the fuel pump. If it starts out at higher speed (AIR) and then slows down (pumping fuel) check the fuel system for a leak allowing air into the system. Could be low fuel level in the tank, a crack in the hose, a leak at the fuel filter.
larry_cad
Explorer II
Jan 31, 2022
How sure are you that the shop actually changed the fuel filter? Maybe just billed you for it and "forget" to actually do it?
Reisender
Nomad
Jan 31, 2022
hotjag1 wrote:
Thanks for the replies. I will start looking for a fuel restriction somewhere in the line tomorrow.

The code light flashes 3 times. The label beside it says "needs servicing". No kidding...lol

I will check the run time tomorrow after I get out of the dentist.
The microwave and or coffee machine work fine while the generator is running, so I don't think there is a voltage issue.

Yep. Good luck at the dentist. But time the run time to failure to the second.

Cheers.
CA_Traveler
Explorer III
Jan 31, 2022
Read the manual and get the second code which will help. :@

The microwave and or coffee machine work fine while the generator is running, so I don't think there is a voltage issue.
These appliances may have a wide tolerance of voltage variation. What is the AC voltage? :h
hotjag1
Explorer II
Jan 31, 2022
Thanks for the replies. I will start looking for a fuel restriction somewhere in the line tomorrow.

The code light flashes 3 times. The label beside it says "needs servicing". No kidding...lol

I will check the run time tomorrow after I get out of the dentist.
The microwave and or coffee machine work fine while the generator is running, so I don't think there is a voltage issue.

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Onan diesel generator quits after a few minuthes

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