Replacement for Onan 4000

Hi CodyClassB,

I did not read through all the replies, so maybe this was covered.

Before spending a penny, before taking the rig in for generator service, first try these two things.

#1 - On your Onan, set the altitude adjustment to the proper altitude. It looks like this.


#2 - Many people don't know how to properly work the "prime" feature.

At your generator control panel, be very quiet. To prime the generator, you must push in the start switch in, but in the opposing direction (it is a rocker switch). HOLD it there and listen for any kind of sound. It would be the sound of the fuel pump running. If you hear nothing, have a family member press and hold it while you are outside under your Onan.

If you don't hear any hum or buzzing sound, then your fuel pump is not working. Check fuses and such. If your hear a hum or buzz, then your fuel pump works.

Then make sure your main fuel tank is at least 1/2 full.

People don't realize how long they need to hold in the prime button to get fuel from the main fuel tank to their Onan. Each rig is different pending the distance between them.

Prime, prime, prime. I advise to do as I do. Hold in the prime button for 15 seconds the first time and then try to start the Onan. If nothing happens, hold the prime button in for 10 seconds thereafter and repeat until it starts.

I never ever run my generator during the off season. I put the rig away in the fall and start everything up in the spring time. A few years, our rig will sit an extra year, and everything always starts right up. I do maintain the batteries during off season. This has been my practice with our rig for 13 years. We do store our rig indoors in a climate controlled environment which I am sure makes some difference. But I never understood all the talk about monthly start-ups and such, though some necessity if the rig is stored in the worst of conditions.

klutchdust wrote:
It would be interesting to know what exactly failed in some of the Onan generators and what it cost to repair. I find it curious that some have had multiple Onan's yet experienced failures in each one and others seem to have outstanding service using them. What occurred that would lead someone to not ever want to own one even if for free. As I have said, my company had no less than 500 units powering refrigeration units and other than normal maintenance were not in the shop unless they were getting a rebuild.

It is well known that any brand of generator in constant use will fare much better than an occasionally used genset.

For people that follow the forums the usual culprits are the carburetor and oil pressure sensor. If the circuit board goes out then it is $$$$$$$ for a replacement. I would offer a far superior replacement board if they have one for your genset.

https://pantherrvproducts.com/dinosaur-elect-300-3763-replacement-onan-generator-board/?gclid=EAIaIQobChMI5ob5zufO6AIVERgMCh3ktgi2EAQYAyABEgIRqfD_BwE

It would be interesting to know what exactly failed in some of the Onan generators and what it cost to repair. I find it curious that some have had multiple Onan's yet experienced failures in each one and others seem to have outstanding service using them. What occurred that would lead someone to not ever want to own one even if for free. As I have said, my company had no less than 500 units powering refrigeration units and other than normal maintenance were not in the shop unless they were getting a rebuild.

True story. Several years ago I stopped at a RV generator shop in Flagstaff to repair my 4000 watt Onan that would quit running intermittent. Problem fixed with a new fuel pump. My Onan had around 450 hrs on at the time. I was telling the technician that we had a RV Club member that had 1450 hrs on his Onan. The tech said that a properly maintained Onan would last a lot longer than that. He said that north of Flagstaff is an Indian Reservation and all the homes are off the grid. He said that he maintains many Onan generators at these home sites that provide electric power on a 24/7 basis - generators running continuously except stopping for oil changes. These were 4000 watt Omans converted to propane fuel. He said he has one Onan that he services that currently had 38,000 hrs on it. Can anyone out there top that?

Double Dose your fuel with Stabil, and you should never have a problem, as long as you run it every 2 to 3 months. I have been doing this for 11 years with my 4000.

I especially like this comment by grit Dog

"Just stop taking it places that charge $300 to replace a $30-60 carburetor. "

There are mobile mechanics out there that are ready and willing to work on just about anything.

I would suggest that one seeks out a mechanic in their area and check out their services and cost.

Now, I had my rototiller give me issues after storage even though I had fuel additive in the gas.

A product called mechanic in a bottle was suggested and is available at the big box orange store.

Well, as skeptical as I am i purchased, followed instructions and guess what, it idled smooth as

silk.

You can buy a replacement carburetor on eBay for less than $40.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2512315.m570.l1311.R4.TR11.TRC2.A0.H1.Xonan+4000.TRS0&_nkw=onan+4000+carburetor&_sacat=0

It’s understandable not everyone has the spare time to exercise their stored vehicles, tools, equipment and toys.
If I did it monthly to every engine that gets used seasonally, I’d have an average of at least a dozen items to fire up, year round, every month.
Proper maintenance and the most applicable combination of fuel care from drain/run dry to stabilize the fuel to use fuel that can handle long term storage is the key.
I’ve used Onan built in generators , never owned one or more to develop a personal opinion on their reliability, so cannot comment specifically to those that take proper care and still have issues, but I would bet that a lot of the issues are due to lack of maint/storage technique vs being inherently unreliable.

I have had motorhomes off and (mostly) on for almost forty years now and have had an Onan problem one time. I forgot that they shut off if the gas level in the rv tank is about 1/4 or less full. About means about I found out.

Fortunately, I live in an area where I can store my C within a few miles of my home and our winters are a few days cold, a few days nice for the entire season. So, on a nice day around the first of the month every month I get it out of storage and drive up the highway about 30 miles with the generator running and under load. I stop, eat a burger for lunch in the little town up the road, drive back to the storage and another month's maintenance on the rv and generator is done. One sixty mile trip and a couple of hours time including a burger and fries is a small price to pay to keep my rig ready for travel season.

Of course, I change the generator oil, change or clean the filter and do all the other normal maintenance as required as well but I have concluded that exercising it is a cheap price to pay.

There is give and take in life. Pulling a cord is a small inconvenience. Knowing that you have a 99.999% chance that you will have power while boondocking is important to me. Nothing stinks more than when you need power and it doesn't work. I constantly had issues with my LP 3600/4000 Onan with updated maintenance (probably over maintained) and religiously exercised. How many times does it take to give up on a piece of equipment that constantly lets you down? Usually I'm not one to give up on equipment but this Onan was not the first one to give me problems. Friends and family that are mechanics also complained about the problems with their Onan generators. The Honda's that I purchased (2000's) I converted to LP and work very well, sip LP, are super quiet, portable if needed, low vibration, last forever, low maintenance (don't need exercised), only have to run one gen set most of the time unless you need AC, etc. I am very happy with my decision.