Onan 4000 Generator - Want To Replace - Alternative?

After 17 years of ownership, I have come to the point with our Onan 4000 generator, where I need to invest in a carb (or maybe more) it to get it running properly and reliably.  I could do that, but I really would like to replace this noise maker with a very quiet, very tollerant, non-fussy, extremely reliable alternative.

Has anyone found such a "Magic Genny" that takes up the same space as an Onan 4000?

This?

https://apelectric.com/content/PDF/RVMP/rvmp_4000i_spec_sheet.pdf


Or a magic silent generator?

https://www.phoenixusarv.com/blog

Or just buy a Chinese replacement carburetor for $25. If you use a little bit of gasket cement to keep them from falling out while aligning the bolts you can do the swap in under 90 minutes .

You could also remove the original  carburetor and clean the jets and float valve with spray Gumout, but be aware that if you  drill out the tamper proof caps to remove all the jets, Cummins - Onan will no longer service the genset, if that matters LOL. Just remember to count the exact number of turns to bottom before removing the jets. The main is underneath  the altitude adjustment knob.
Be sure to spray the fuel shutoff solenoid valve thoroughly, and actuate it with 12v to check that it moves freely before reassembling.

Interesting about that other brand.

I would love to have a fuel injected generator.

New from Cummins. 

https://www.perplexity.ai/search/new-4k-onan-inverter-generator-kaxw3JJrSTGHgF.lW400pw

https://www.cummins.com/generators/onan-qg-4000i

They are not yet shipping them.  And when they finally become available, the OEMs will likely get them first.

Ron

Well, I decided to go the easy route and pass off my generator trouble to a Cummins professional.  Today was "Cummins Onan 4000 Day."

I drove over to the official Cummins service center in Oak Creek, WI this morning and handed over my motorhome. 7 hours later, I headed back home.

During my times of operational trouble with the generator, I did have a backfire that resulted in a brief contained fire that deformed the plastic piece that shrouds the air filter.  That plastic piece is huge, requiring the technician to remove the generator from the motorhome to replace it. Here was the cost break-down.

$534 - OEM carburetor
$38 - large plastic shroud (includes carb inlet and air filter housing)
$1154 - labor
$1828 - total with taxes and a few other misc

Ouch! as expected.

I have to say that the generator runs perfect, possibly even better than when the rig was brand new. At least I got that out of it.

Talking with the tech afterward, we discussed the following with consideration to Illinois mandate of 10% ethanol in all their regular, mid-grade, and premium fuels.

- add Sta-Bil
- add fuel cut-off valve
- utilize carb drain screw

He basically recommended utilizing all 3.  I will be practicing this after every trip which he said should be good for extra long-term storage.

1) Fill the main tank to the top, add adequate Sta-bil (10% ethanol may require extra Sta-Bil).
2) Run the generator for 15 minutes to get the Sta-bil'd fuel throughout the carb passages to protect it from the 10% ethanol.
3) Cut-off the fuel and let the engine run-out til it dies.
4) Drain out what little remains in the carburetor bowl, utilizing the carb drain screw.

Hi Ron...  So on our spring trip this year, I installed the cut-off valve you had suggested in an earlier thread.  I think I added a can of Sea Foam rather than Sta-Bil, I had never used that, and noted the can says it can be used as both cleaner and stabilizer.  And I followed all the other suggestions from the Cummins tech, except #1.

The first couple years I had my PC, I was filling the fuel tank prior to going into storage, as he suggested.  After a couple years, I noticed that my mileage on that first tank was always significantly worse, like 7 mpg.  Then from the 2nd tank onward, it would be more like 9 mpg.
So I started leaving the tank as empty as possible, rather than full, and the first stop coming out of storage was to fill the tank, at which time I would also add some Techron injector cleaner or equivalent.  That seemed to help the low mileage on the first tank, which was 6-month old fuel at that point.

Hi Rick,

The issue storing any vehicle with an empty gas tank, is accumulated moisture.  The less air space, the less "tank breathing" from the air/fumes inside the tank. heating and cooling, expanding and contracting during storage.  The evaporation system takes care of fumes being exhausted, but not with humidity entering the tank.  Depending on the envirionment (humidity and temperature swings) you could end up with an accumulation of water inside the fuel tank from long term storage.

I top off my tank after every trip to assure there is as little air remaining inside the gas tank as possible.  Since most often, I don't know when our next trip will be, I treat every end-of-trip the same.



One other point about this subject.  This applies to my 2007, but not to later model years.  NEVER allow your fuel gauge to go below 1/4 full to specifically maintain the integrity of the fuel pump inside the fuel tank.  Once the elecric fuel pump is fully exposed above the level of fuel, it runs hotter which reduces it's life.  A cooler fuel pump is a healthier one.

Here is a picture of a 2007 E450 fuel pump assembly.  Note the fuel pump is at the bottom.

Here is a picture of a 2015.  Note the pump is inside a plastic bucket, kept full even when the tank is just about empty.  The design was improved to address the condition.

Ron, for future reference.  The gen can be lowered very easily with a motorcycle jack. If you know anyone who rides they probably have one you can borrow. If you don’t have levelers run your drivers side up on blocks to give you more room after you lower the unit. Once down replacing that plastic is easy. I went thru the same problems you have . A fuel shut off didn’t work. There almost all plastic and leak by.  I installed a $25-40 carb from Amazon, then I purchased a Chinese fuel pump for around $ 20 if I recall. Purchased a second one as a back up. Then I relocated the fuel pump to just out side the casing where the fuel line came in. From that I installed a kill switch .

After running the  gen I simply cut power to the fuel pump and run it dry. Before I did the fuel pump location and power switch I fought with it every year.  I’ve been fighting cancer for over 2 years so it sat for almost a year and a half. Started right up and ran smooth.  This after replacing the carb at least 3 times. I was a slow learner. Part of the issue is the pump location, it gets blistering hot. Sometime causes  vapor locks, sometimes caused reduced flow and so on. I have yet to have an issue since making these changes. Fuel filter, fuel pump, new carb, switch, 5-6 inch longer fuel line and done for less one Benjamin.  That’s without your plastic part however and I borrowed a motorcycle jack.  Now should a fuel pump go bad I could change it out in 10-15 minutes.


It all started however when my starrier went bad. I had to drop the gen to change it out. I was already fighting what I thought was all carb issue. Just made sense to try it all while it was already lowered.

Very interesting Joseph.  Thank you for this insight and experience.  I will keep that in mind if there is ever a "Next Time."  I have read on other forums of people relocating the electric fuel pump outside the Onan, but your idea of adding an electric kill switch for it is "Very" logical.

I had previously decided to add a quarter-turn fuel cut-off valve as shown.  It took all of about 5 minutes to install.  I considered also adding a fuel filter in-line there, but decided against it for fire safety....call me paranoid now.  Hopefully the valve I chose won't leak by as you had experienced, allowing fuel into the carburetor during storage.


I chose a metal 1/4 turn valve over a plastic one, thinking it being the better of the two choices I had on-hand.  I had wondered if the handle being so long, it might vibrate to the closed position, but there is a lot of built-in resistance.  If it later becomes a problem I could always add a slip-ring to attach the handle to the fuel line.



I ran the generator until it died, then loosed the bowl-drain screw to see what remained inside which was just a few drops of gas.

That metal valve is light years ahead of the plastic one.  Just keep the info I gave you in the back do your mind should you ever need to change out your starter.  Moving your fuel pump should you ever want, you do not need to drop the Gen set.

That metal valve is light years ahead of the plastic one.  Just keep the info I gave you in the back do your mind should you ever need to change out your starter.  Moving your fuel pump should you ever want, you do not need to drop the Gen set.

Well...SUPER late to this party... Glad you sorted things out.

but as to the original question -

""Has anyone found such a "Magic Genny" that takes up the same space as an Onan 4000?""

As usual, I wont be using readily workable, or generally approved parts and methods. 



The noise from the onboard genset is intolerable for us. Runs well, and gets the job done..... but loud outside and in. I try to remember to exercise it at least once a month.. or two... (Hm.... might just go start that and let it run for a while this evening...)

I now use the Predator 3500, a Honda 'clone' from harbor freight. If we are at a smaller gig, I use a hitch mount rack and put the genset on it. The genset running on that rack is much (MUCH) quieter, and much less vibration. Even right under our heads in bed! Or put the genset on the ground... cant hear it over the AC. Sips gas. (I get 7-8  hrs on a 2 1/2 gallon tank running AC all night)

Will not run the AC and Micro together, but thats OK.  We rarely microwave, and just turn off the AC when we do. Runs AC, fridge and converter loads together with no problem.


Having two of these gensets now, and tinkering on them, I am working out how to replace the Onan with a predator. Electric start already built in... thats a big plus. Weighs 100 pound WITH a tank, little more than 1/2 the weight of the onan.

OF course, I cannot recommend this modification to be done by anyone. Critical safety features built on to the Onan may be difficult or impossible to duplicate safely. The Predator genset is not designed for this use, and undoubtedly the manufacturer would agree it can not be used installed like I discuss.




So please, dont try this at home.      

Volkemon, like with all your other modifications, repairs, and updates, please keep us posted on your Predetor 3500 installation.  I really enjoy all your share and the details.

On the irv2 forum, I have this same post running there.  Someone there shared a new product, just posting it here for consolidation purposes.  I really know nothing about it other than watching the short video.
https://npsrvpower.com/
Admittedly, the product confuses me.  Generator and sine wave inverter, all in one?  My traditional thinking is to have the generator focus on one thing, make household electricity, then let the RV on-board systems break it down from there.

The enclosed generator is a very tough environment with heat and vibration.  All that "other" technology integrated inside it seems risky to me.  Then there is the price tag, another discouragement.

I started carrying 2 of the Yamaha 2000 gensets. I went that route due to weight. Easier for me to handle two lighter weight units than one big heavy one. This was before I found my Onan issue and fixed it for good.

Two things happened at campgrounds. When under AC load they were quieter for us in the motorhome but not for other campers. No heavy load no issue, AC and other campers wanted it located right up against our RV.  The next was when another camper had his stolen. They cut the steel cable, loaded it up and gone before he could get wake up enough to know he had a problem. I finally fixed my onan issue and got rid of the portable.

Your idea of installing where the onan is may work great. One of the things that makes them quiet is their casing. My concern would be them getting enough air flow in that compartment. If you remove the cover it will be louder. Maybe an auxiliary fan to maintain airflow. Also once mounted it will have its own vibration tendency.