Community Forums

Trek8288 · 03-20-2023, 07:48 AM

I have an Onan 4000 GENERATOR in my Class A motorhome. It is using oil, more than usual. (I use 15/40W as stated in the Onan guide). Is is now getting weak, that is It is tired. (Prior owner never really drove it much, as you can tell by miles), but ran generator alot.

My Motorhome in a Fleetwood Class A 32 workhorse, 2002. I have had it going on 4 years now, has just at 22000 miles on it, (yes original). However, the generator has much more hours.

Considering pulling generator and overhauling it. ? (your thoughts).

Considering getting a used on. (thoughts)

Considering a new one. ? (thoughts). Would a 4500 be a direct replacement?

Is there a better choice.

TandW · 03-20-2023, 03:07 PM

Run it with high mileage motor oils or straight 40 weight until it throws a rod. Everything about it is old.

rguild · 03-20-2023, 03:40 PM

I recommend you locate and set an appointment with a Cummins Onan Sales and Service center. I’m over 5 years out as a full timer and developed similar problems with my Onan 5500 RV. if you refer to you owner’s manual you will find how to display an error code. That’s a starting point to diagnosis.

That said I spent over $700 at two shops representing themselves as Onan service qualified. The last referred me to a Cummins Onan service center, which finally fixed my problem.

ga traveler · 03-20-2023, 03:59 PM

Quote:

Originally Posted by TandW

Run it with high mileage motor oils or straight 40 weight until it throws a rod. Everything about it is old.

I highly disagree with this. Your engine is designed to run on a 15 weight oil. The 15W 40 means it is a 15 wt oil that has viscosity enhancers to protect like a 40 wt. a 40 wt would be almost thee times a thick as the oil it was designed for.
I went to Onan factory school on the Onan generators. They do approve straight 30 oil in Onan generators when the temperatures over 32 degrees.
I would go to straight 30 wt. I have used straight 30 wt in my generator for 16 years without any problems.
Do you cool your generator before shutdown? Onan recommends running the engine 4 or 5 minutes after removing the load from it. If you shut it off under load, the temp will rise and cook oil on the cylinder walls. This will cause it to start using oil.
The first thing I would do is to run some sea foam through the air intake. Then switch to 30 wt oil.
If you decide to do this let us know how it comes out.

Mudfrog · 03-20-2023, 05:59 PM

I don't think I'd run it with straight 40w but I might try a single viscosity 30w conventional oil to see if it helps slow the oil consumption. Probably won't do a whole lot but ya never know.

The single grade 30w oil is actually what's recommended for my built in 2002 Onan 4000 and is the only oil I've ever used. Of course, I'm down here in southeast Texas where it's rare for temps to go below freezing.

shootist · 03-20-2023, 06:07 PM

I’m in the run it until it dies and replace it. Engines are cheap to rebuild if you do it yourself. But not worth swapping or rebuilding when paying a shop as the generator and controls are all old as well. I just finished rebuilding a generator on a Miller bobcat 225 welder. 500$ to have just the 240 end of the stator rewound. Very low hour machine so well worth it. Stick with the 15/40. It’s 15 weight on startup and is slightly thicker than 30 weight at 180 degrees.

donr103 · 03-20-2023, 07:12 PM

You tell us everything but hrs on generator and how many owners.. is it making a noise ??
Good luck and keep us posted

johnhicks · 03-20-2023, 08:15 PM

An Onan QG4000 will cost around $6,000 plus labor. No idea now how obtainable they area.

I strongly suggest you go to an official Cummins/Onan shop and have them look at it. And don't use any oil other than SAE 30 or 15w-40.

Isaac-1 · 03-20-2023, 11:05 PM

Quote:

Originally Posted by johnhicks

An Onan QG4000 will cost around $6,000 plus labor. No idea now how obtainable they area.

I strongly suggest you go to an official Cummins/Onan shop and have them look at it. And don't use any oil other than SAE 30 or 15w-40.

Where do you get $6,000, Norwall's has them for $4018 with free delivery

SavnTheWales · 03-21-2023, 12:33 AM

Maybe it just need rings.

Trek8288 · 03-21-2023, 07:33 AM

Multi-grade oils (such as SAE 15W-40) are recommended for year-round use in Cummins Onan liquid-cooled engines, or as a good all-season oil for air-cooled engines. NOTE: SAE-30 is the preferred summer grade for optimum oil consumption control in Cummins Onan air-cooled engines. Jul 18, 2020. This is a quote from Onan.

I called Onan regarding this. I was advised that Onan's previous recomendation was for use of only SAE-30W oils, non-synthetic. But due to the advancement in oils they have given a chart on recommended oils which also is Synthetic Blend, (Not Full Synthetic).

I was using only 30W oil in the generator until it started using above normal amount of oil. Then on recommendation from Onan I switched to 15W-40W Synthetic Blend which did lesson the oil use, (for about a year). Now the use of oil is just too much; I add oil every few days now.

I wish to add, I DO NOT reside in a harsh environment. I am in California where the temperatures are well within mild temperatures. (At least for now). I had planned on getting on the road and just traveling around for a few years then the pandemic hit :( . (I am 71).

Now the generator is not generating enough power, (the last couple of weeks); that is, if I run the microwave now the generator will shut down. So, I will run the engine also which gives it a boost. However, the last few days unless I run the generator for about 1/2 to 1 hour, then run the engine also, it will shut down when a load is on it.

It is tired. The hour gauge show 4049 hours. I do not know the range of projected hours.

Mudfrog · 03-21-2023, 07:58 AM

An Onan with 4049 hours is just getting broken in. Actually not, but it still isn't that much on a well taken care of genset. But of course, there's the rub,, who knows how well it was maintained all the years before the OP got it.

I'd lean towards having it checked out and possibly rebuilt. Maybe just a quick piston pull and new rings installed? Cleaning the sucker out, checking/tightening wiring and connections, and/or installing new brushes might be all that's needed power wise.

Isaac-1 · 03-21-2023, 08:29 AM

I must disagree here 4049 hours on an Onan KY 4000 which runs at 3600 rpms is a lot of hours, for some of the larger 1800 rpm Onans 4049 hours is only mid life, but not in this case.

swduns · 03-21-2023, 08:30 AM

I agree with the previous post, 4000 hours is nothing. the worst thing for a generator is to not use it.

This is my 3rd motorhome and onan generator. The first 2 gas generators, I had issues and pulled them both and took them to Onan/cummins dealer both twice. Paid about $1000 each time and they claimed they fixed them but each time the same problem returned. I ended up fixing them myself. I have had very poor experience with Onan/cummins dealer repair.

I called Flight Systems, inc. https://www.flightsystems.com/ 517-590-7330 there is a way on their web site to set up a one on one troubleshooting call, all for free. Flight systems sells aftermarket repair parts of Onan, they claim better than Onan. but every time I had a Onan generator problem they talked me through troubleshooting the problem. sometimes it took several calls to go back and check what they told me to check. The last time it turned out the problem was the crankshaft position sensor, once I changed it the problems went away and never came back.

maybe there is a simple explanation for the excessive oil usage. maybe the generator output is the voltage regulator .... they can help you figure it out

my advice call flight systems ....