Cummins Onan RV Generators: They Should Just Run, Shouldn’t They?

Cummins Onan RV QG 2800 generator
Onan RV QG 2800 generator

Note: I get commissions for purchases made through links in this post.

Cummins Onan (aka, Cummins Power Systems, since the early 1990s) nearly has a monopoly on the recreational vehicle (RV) market when it comes to generators. They still put just “Onan” on the machines themselves, and you will still see mention of Onan RV generators online and in print.

With the many years of experience that Cummins has had with these portable generators, you would think all their machines would work like a charm, wouldn’t you?

Many owners will take issue with that. Let’s see if we can find out why.

If you’re in a hurry and just want to check the pricing and availability of some of the Onan generators at Amazon, you can click the links below. (Cummins Onan produces more than the unit in this short list, as you’ll see below if you keep reading.)

If you do have time to read but want to skip ahead to a certain section of this article, you can click a link in the box below.

Which Gas Generators Does Cummins Offer?

Cummins Onan gas generators, which are probably the type of rv generator that you as a typical consumer would be interested in, come in 3 flavors – gasoline powered, liquid propane (LP) powered, and electronic fuel injected (EFI) models.

The tables below compare several of the features of the following models, so you can see at a glance which one would be of the most interest to you.

That said, Cummins doesn’t make it really easy to compare models like this. Numbers in parentheses refer to LP usage apparently of the same model that uses gasoline.

ModelQG2800 RM (QG2500 RM LP)QG2800 (QG2500 LP)QG4000 (QG3600 LP)
Watts2800 (2500)2800 (2500)4000 (3600)
Weight (lbs.)107113172
LxWxH (in.)19.6 x 16.7 x 12.324 x 16.4 x 12.330 x 19.7 x 14.4
Fuel Consumption* (gal/hr)0.3 (1.5)0.3 (1.5)0.5 (2.4)
Air Conditioner** (BTU)One 13,500 (HE)One 13,500 (HE)One 15,000
Cylinders / Type1 / OHV1 / OHV1 / OHV
Cooling SystemAirAirAir
Decibels* (at 10 ft.)727266

*Half load
**HE – High Efficiency Air Conditioner required.

ModelQG5500 (QG5500 LP)QG5500 EFIQG7000 (QG6500 LP)QG7000 EFI
Watts550055007000 (6500)7000
Weight (lbs.)279279290290
LxWxH (in.)33.6 x 22.2 x 16.733.6 x 22.2 x 16.733.6 x 22.2 16.733.6 x 22.2 x 16.7
Fuel Consumption* (gal/hr)0.6 (3.3)0.60.7 (3.5)0.7
Air Conditioner (BTU)Two 15,000Two 15,000Two 15,000Two 15,000
Cylinders / Type2 / V-twin2 / V-twin2 / V-twin2 / V-twin
Cooling SystemAirAirAirAir
Decibels* (at 10 ft.)69697070

*Half load

Which Diesel Generators Does Cummins Have?

The diesel Onan generators (QD) are generally larger in size and power capabilities than the QG models above. Here is what Cummins offers currently.

Weight (lbs.)205420420
LxWxH (in.)30.2 x 17.3 x 18.036.3 x 23.6 x 22.336.3 x 23.6 x 22.3
Fuel Consumption* (gal/hr)
Air Conditioner (BTU)One 13,500Two 15,000Two 15,000
Cylinders / Type3 / Inline3 / Inline3 / Inline
Cooling SystemAirLiquidLiquid
Decibels* (at 10 ft.)716666

*Half load

Weight (lbs.)765770
LxWxH (in.)41.4 x 24.5 x 27.041.4 x 24.5 x 27.0
Fuel Consumption* (gal/hr)0.430.48
Air Conditioner (BTU)Three 15,000Three 15,000
Cylinders / Type3 / Inline3 / Inline
Cooling SystemLiquidLiquid
Decibels* (at 10 ft.)6869

*Half load

What Do Owners Think of Cummins Onan Generators?

Many owners have complaints about their Onan generators. I won’t repeat them here. They’re easy to find elsewhere if you really want to see them.

What I will quote for you is what an owner who has had no problems with his unit in 5 years of usage has said. (I have edited the quotation below slightly for clarity and grammar.)

“I read that many are having problems with the Onan 5500 watt gen. We have owned ours for 5 years without a hitch. My dealer gave me a tip years ago how to maintain an Onan and get years of life from it. First of all, our fuels or gasolines being processed in the USA are the poorest quality in years. It’s trash and the generators get the bad rap. I pour in a can of Sea Foam per 20 gallons and put a heavy load on it for 30 minutes. Everything, roof air, electric hot water heat, etc. This opens the throat of the carb and cleans the crap out of it. It is good for your chassis engine also, makes it idle much smoother. Try this procedure and see what I’m seeing.

“PS. One other tip. If your gen has been sitting unstarted for a while, pull the cover from it and start it remotely. When cranking the engine over, the automatic choke will wiggle lazily and can’t pull the fuel to the main jet. If you push and hold the choke away from you, it will start in 3 seconds. I guarantee it. I hope this gets you started and enjoy your camping.”

I understand that there is some maintenance required with portable generators, but this seems excessive. An engine should not require that much attention. I know it’s not comparing apples to apples, but what if my lawnmower engine needed all that?

I’m also not sure how some users can say their Cummins generator is quiet and others say it’s noisy when talking about the same model. “Noisy” can be a relative term, but there shouldn’t be that much difference.

I’m wondering if maybe Cummins has some quality control problems, and that’s why we see such discrepancies in comments about the same or similar models of generators.

Another possibility is that some of the owners who are having the problems are not starting with brand new machines. Perhaps they got one second-hand from someone who didn’t maintain it properly.

What’s the Verdict on Cummins Onan RV Generators?

If the RV you purchase already has an Onan generator installed, which seems like a good possibility, be sure to ask how old it is and if it has been properly maintained while at the dealership (or wherever you buy your RV).

If it’s brand new or is still in tip top shape because someone knew how to care for it, you should have no qualms about your purchase.

The same can be said about buying just a brand new Onan generator by itself.

By wary though if you can’t find out the history of the machine. You might just be asking for trouble, and trouble is probably what you will receive.

Click the links below to see these generators at Amazon.

Cummins Onan RV QG 2800

Cummins Onan RV QG 5500

Cummins Onan RV QG 7000

If Cummins Onan doesn’t have what you want, maybe this Champion is more what you’re looking for.