Onan Generator 4000w Cuts off after running a while

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OTGT

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I am new to this forum so there are several questions I have. My 1990 Fleetwood Flair has a 4000w Onan Generator that runs great but for some reason after a while (sometimes 30 minutes - sometimes several hours, it cuts off and is imposible to start for a while. Its not a fuel issue because I have a full tank. Any suggestions? ???
 
Have you checked how long the generator runs under various load conditions? If it runs shorter on a heavy load and longer on a light one I would suspect it may be overheating. I believe my Onan 6.5 kw has a thermal switch to prevent over heating.

After you've eliminated the load as the problem, try to monitor the temperature inside the compartment. Does it crap out early on hot days?
 
When it cuts off, maybe you can check the last point the fuel enters the carb (I assume it is gas gasoline), and the carb bowll should have a drain that you can check to see if there is fuel present.  I would be suspicious of fuel starvation.  Every problem I have ever had with my two portable gas gen sets have always been related to fuel.
 
Mine has a low oil cutoff. Never thought of that.

I did have an issue last year when I first got it with dirt in the gas clogging the fuel filter as well.

 
Thanks for the many suggestions, I have it in the shop at the moment to replace the main LP Valve and will chech this once I get it back.  I'm new to RV'ing so please forgive me if I ask dumb questions.
 
I just got done changing the generator Oil and Oil Filter and It started working fine again.  I use an original Onan oil filter and castrol 30w HD (high detergent) oil. I didnt change the air filter nor the plugs because they looked ok. What the problem actually was is that the oil that was in there had too many hours on it and was dirty and just needed new oil. The dirty oil caused the low oil pressure sensor to shut down the generator. Just for your information, my generator is a Onan Emerald Plus 4000watt gen.

Thanks for everyones help. :)
 
John Canfield said:
When it cuts off, maybe you can check the last point the fuel enters the carb (I assume it is gas gasoline), and the carb bowll should have a drain that you can check to see if there is fuel present.  I would be suspicious of fuel starvation.  Every problem I have ever had with my two portable gas gen sets have always been related to fuel.
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Ok I changed the oil and filter and it definitely started to run much better. BUT, I noticed that it will run forever and a day while the motorhove is standing still and the engine off. When im going down the road with the AC on low, it will randomly turn off. But since the oiil change. It will start right back up and run for a while again. I dont think its a low oil pressure issue because it will fire up everytime. I also think it may be shutting down under a medium to high load. It seems to stay ON better if im just running the roof fan instead of the AC. What do I need to check for now?
 
That sure suggests that the oil is foaming, resulting in low oil pressure and a shutdown. Maybe the combination of movement and high load are producing enough foaming to shut it off occasionally.  I've heard that a high oil level can cause foaming. Maybe try a  little bit less oil?  By the way: when you changed the oil, did you go by the dipstick or add exactly the amount the spec calls for? Do the two amounts match?
 
Reasonable point, Gary. I can add a bit of info here. On my 1994 5KW Onan, the dipstick measurement is critical.  The manual states that the dipstick plug must be screwed all the way in to get the proper reading. (Not just dipped as on other dipsticks). If this is not down that could result in an extra quart of oil being added.

  I just changed my oil a couple of days ago. 3 1/2 quarts (capacity) showed perfect on the dipstick.

  Just another thought...

carson FL

 
RV Roamer said:
That sure suggests that the oil is foaming, resulting in low oil pressure and a shutdown. Maybe the combination of movement and high load are producing enough foaming to shut it off occasionally.  I've heard that a high oil level can cause foaming. Maybe try a  little bit less oil?  By the way: when you changed the oil, did you go by the dipstick or add exactly the amount the spec calls for? Do the two amounts match?
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I just changed the oil about a week ago and like I said it runs better for sure. When I changed the oil, I completely drained the oil out and added the required 3.5 Quarts of oil. I dont think I even checked the dipstick after I added the oil but I will definitely do that. Someone told me I need to replace the fuel line and filter because they can get clogged over time and with the engine putting preassure on the lines, it may be causing the fuel not to flow properly.
 
OK, Problem Solved. It turned out it was a weak - worn out fuel pump. What was happening is that when the MH was still, the pump was just strong enough to keep the fuel pumping. But when the MH was moving, It was not strong enough to pump the fuel as the fuel sloshed around. Basically, the fuel was being siphoned when still. Hope this help if anyone else is having similar issues.
 
Fuselier65 said:
onan 4k generator runs fine 30 min the put ac on runs another 30 min and stops
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Fuselier, the post you tagged on to is from 2009. You would be better off starting a new post (Click on "New Topic") (just before the list of topics above) and describe your problem with more detail, including the Model number, year etc of the Onan and the load you have applied when this happens.
 
Mine had a similar problem, the inside of the hose had flaked off and stopped up the fuel entrance at the needle and seat.
 
Having just gone through this issue (runs while sitting- quits when on the road) I would suggest that it probably has nothing to do with the oil or oil sensor. I chased that for months. Cummins assures me that is not critical & will not cause a failure while moving like described here. We went through everything with mine, including filters, new fuel line & two replacement fuel pumps & the real culprit turned out to be a faulty carburetor that was not properly regulating the fuel flow, allowing it to slosh around in the carburetor while moving & causing vaporization from the gas on hot carburetor walls. Replacing the carburetor was the fix. My generator is a new(2015) 7000 KW.
 
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