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Old 07-31-2018, 01:38 PM   #1
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Cummins Onan generators 101

Attachment 213306

I decided to post this topic to hopefully help educate the RV going public about how to properly operate, maintain and take care of your Onan generator for years of trouble free performance. Many of the common problems I have seen on these forums are often more than not a lack of knowledge in how to properly operate and care for your generator.

First off a basic knowledge of understanding how your generator works will help you have better success in enjoying it's use.

Most Onan generators are powered by a gas driven motor that will run on low to mid grade gas with a carburetor and basic manual choke. It's important to run fuel stabilizer through your genset everytime you use it to prevent lacquer buildup in the fuel lines and carburetor. A stuck float in the carburetor bowl or stuck choke will cause you endless possibility of performance problems. That's why it's also important to replace the fuel filter regularly at manufacture specification. So the rule of thumb keep your fuel system clean. As a general rule Onan generators might run better in hot weather rather than cold. In cold weather you might have to help the genset along until you get it at full operating speed. Many people forget these require manual priming. If your Onan doesn't have the feature that will prime the system when you hold down on the stop button, you may want to consider installing an inline primer bulb. This is where a lot of people run into trouble with starting issues, and it can save you a major headache. Note: that you may have to prime the system two or three times while trying to start it for the first time before the motor will actually start. Remember the gas has to get from the fuel tank all the way up to the Onan's carburetor. Don't forget to check the operating condition of the fuel pump often. A bad fuel pump will defiantly cause starting issues.

Number 2. The engine. The engine is connected to the turbine mechanism via the mounting bolt on the fly wheel. It is recommended by Cummins that the motor oil be changed every 50 hours of use. In my experience a typical 10w 30 weight SAE motor oil will work just fine. Anything heavier could damage the engine as these are only a two cylinder engine, so take heed. In addition don't forget to check spark plugs. There are usually two on an Onan. Check wires and replace your oil filter anytime you replace the oil. It's also important to replace the air filter on regular intervals.

3. Turbine and stator mechanism.
As the engine turns at a speed of almost 5400 RPMs the stator, the magnetic brushes ride on a pair of metal slip rings at the end of the stator drum. (You can usually see the the slip rings by shining a flashlight up into the vent holes.) When you turn the AC breaker on, on the side of the generator this engages the magnetic action between brushes and slip rings. This is the magic that then sends AC power to your RV through your RVs inverter and in turn powers the lights and appliances in your RV. The brushes are the heart of the system and should anything happen to them you would be left instantly in dark. It is essential to make sure the brushes are always kept in tip top shape to maintain a healthy generator. Please note: in most installations it is your inverter that charges your batteries, not the generator. The generator uses your inverter to charge the batteries. So the inverter and all your breaker switches must be on while the generator is running for the batteries to achieve a full charge. Make sure the inverter and breakers are off whenever you start or stop the generator. Allow your generator to warm up for at least 5 minutes before turning the inverter and breakers on. It is very important to never let your generator run out of gas while it is under load. This can burn up the brushes and slip rings which could cost thousands of dollars to repair the damage. Most importantly. Never leave your generator unattended while it is actually running. If you have a problem turn your inverter breakers off first then the generator until the problem has been corrected. again when you start generator, generator first then inverter and breakers and always in that order.

Don't forget the very important brain of your system. The circuit board. Basically keeping it clean and well protected from the weather is all this component really requires. Occasionally checking all the electrical connections and clean them with compressed air as necessary. Disconnect the house battery before you work on the circuit board so you don't accidentally cause electrical shorts in the system. Many people complain that generator will run for 20 minutes then shut off if it's not under load. The circuit board ( the brain) has a build in fuel saving feature that automatically shut the generator off after 20 minutes if it's not under load. This is the brains way of saving gas if the genset is not actually being used. So keep it under load to keep it running. If the 20 minute problem occurs while under load. Your stator, slip rings and brushes are probably in severe need cleaning. The circuit board does occasionally go bad if it has at all been exposed to weather and may have started corroding. Examine and correct the issue.

I hope this helps. It is my general experience if you Follow the above tips you can enjoy trouble free performance for years to come.
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Old 07-31-2018, 02:52 PM   #2
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Is there a problem with the link? I could not get it to work?
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Old 07-31-2018, 05:42 PM   #3
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Where did you find this information?
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Old 08-02-2018, 10:06 PM   #4
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As an Onan technician I have never heard of a 5400 rpm engine or the 20 minuet shutoff feature.
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Old 08-03-2018, 02:16 AM   #5
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I pull the fuel pump fuse and let the engine empty the carb. I added a prime push button so it will start faster. 1800 rpm with 7 to 1 compression, it will run on farts!
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Old 08-03-2018, 04:23 AM   #6
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As an Onan technician I have never heard of a 5400 rpm engine or the 20 minuet shutoff feature.


And I didnít know they call the alternator a turbine..
and I think he missed the maintenance on the flux capacitor.
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Old 08-03-2018, 04:41 AM   #7
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Guess it depends on the type/size of your Onan. My 4k requires oil changes every 150 hours, does not have an oil filter.

Recommended oil depends on ambient temps.

5w-30 @ -20 to 50
10w-30 @ 0 to 80
10w-40 @ 0 to 80
15w-40 @ 10 to 100
30 @ 32 and higher



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Old 08-20-2018, 09:02 PM   #8
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This post is full of some serious misinformation. Read the manual and do what it says. Most importantly, run it often with a load.
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Old 08-20-2018, 10:36 PM   #9
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A slight correction on the inverter. The inverter converts DC power to 110 volts of regular electricity, so you can operate things like a kettle, or charge your laptop by plugging it in to an outlet. A converter, converts AC regular electricity to DC power. This is what your generator uses to charge your batteries. An inverter takes power from the battery, while a converter runs your 12 volt system and charges your batteries. Dont want to nit pick, but people have a hard enough time understanding this as it is. Cheers
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Old 08-20-2018, 11:48 PM   #10
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Cummins Onan generators 101

Cimplex, with no money spent in Onan R&D on the gas side in a decade. I am done with you, rig powered by Honda EU3000, just starts, and runs & runs & runs @ half your noise. I can charge the rig up and make coffee at near idle. Can you do that? No, you run @ 60 cycles and scream away wasting fuel.I can do with one gallon of gas the same thing it takes you 5 gallons. Go sell crazy somewhere else, I am all stocked up here.
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Old 08-21-2018, 10:03 PM   #11
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Is there some personal grudge between the Diesel team & the gas team at Onan not to share tech? The liquid cooled diesel team had the idle tech for years. But yet a million units of gas went out the door that could have been much better for all of us. I believe some senior management needs to be taken to the wood shed for holding the company & shareholders back from making a great product, money, & a happy costumer base.
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Old 09-03-2018, 06:54 PM   #12
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Quote:
Originally Posted by trx430ex View Post
Cimplex, with no money spent in Onan R&D on the gas side in a decade. I am done with you, rig powered by Honda EU3000, just starts, and runs & runs & runs @ half your noise. I can charge the rig up and make coffee at near idle. Can you do that? No, you run @ 60 cycles and scream away wasting fuel.I can do with one gallon of gas the same thing it takes you 5 gallons. Go sell crazy somewhere else, I am all stocked up here.
Well said. My Onan 5500 has been nothing but trouble from day 1. Randomly quits running, surges at no load, loud, and gas hungry at only only one year old with 114 hrs. I now carry my three Honda 2000 to power the TH.
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Old 09-03-2018, 07:09 PM   #13
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50 hr oil change no need for a primer bulb if it has an electric fuel pump
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Old 09-26-2018, 04:32 PM   #14
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Quote:
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Well said. My Onan 5500 has been nothing but trouble from day 1. Randomly quits running, surges at no load, loud, and gas hungry at only only one year old with 114 hrs. I now carry my three Honda 2000 to power the TH.

Surging??? Hmmmm. You might want to check and see if your choke is sticking shut. Also adjust the governor. An improperly adjusted governor is a common cause as to why these Onan's surge so much. The adjustment screw under the governor linkage. It's much like adjusting a carburetor idler screw. I also learned very quickly when I first started with these, on Onan's you should make sure the choke is all the way open before starting the genny up and that it stays open. Eliminates an awful lot of issues. Your Onan's have a main circuit board at the stop/start button. If the generator can't achieve a smooth idle and continues to surge, the main circuit (the brain) is supposed to shut the generator. The main circuit can also shut the generator down if it runs for more than 20 minutes with no load, in order to save gas. Just the electronics doing their job. Once its running smoothly and under load, it should be able to run for hours if not days and weeks on end. Onan's can provide clean power that is safe for sensitive electronics if you keep it well maintained. My Onan 4000 puts out very clean power.
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