Is Onan Cummins QG Generator 4000i Actually Better than Previous Generation

Updated 08/15/2025 | Published 07/28/2025

Question:

Hello, I’ve bought many things from etrailer, you guys have always been straight up with me . I’m looking for a honest, I mean honest opinion on the new onan 4000i. I have the older 0nan 4000 , it’s so loud I have using it . I boondock a lot in the south… so need ac at night. I bought a RVMP 4000 and was much quieter at first , but is getting louder and kinda clanky . The fuel pump has gone out at 200 hours . , I’m replacing fuel pump , but thinking about selling it . I just don’t trust it I’ve already reinstalled the old Onan . Online -Ai says people are having the same problem with the new Onan. Is this true? My whole question is do you honestly think the new onan 4000i is trustworthy? Quieter and worth the money ? Would you buy one , or wait for a second generation? Thank you Jay 4099397011

asked by: Joseph W

Expert Reply:

Hey Joseph, I'd be glad to help you decide if the 4000i is a solid enough of an upgrade from what you've had in the past including the older 4000 from Onan. Lets go over some of the changes. The new engine is larger and a different design, It’s all new with 389 cc versus previous 304 cc displacement.

The fuel consumption is a lot better. At half load it is 0.27 gallons/hour, which is a big improvement over previous rating of 0.50 at half load.

Noise is 63 dB at no load and 66 dB at half load which doesn't sound (pun intended) like that much of an improvement versus 68 dB at half load. But decibel rating changes are kind of odd to understand. 68 dB is noticeably louder than 66 dB... A 3 dB increase in decibels is generally perceived as a doubling of loudness. Therefore, 68 dB is about 1.3 times louder than 66 dB.

Weight is down 13% which is about 20 pounds.

Generator has no brushes, is fuel injected, and holds more oil which allows it to require fewer oil checks too.

So there are some very solid upgrades to be had that I think going with the 4000i # CM42ZR over what you have now will make you happy.

I've also checked online and tried to find what the overall consensus is with this generator and everything I found on it was that people really like it and its very reliable.

expert reply by: Jameson C

Jameson C.

8/15/2025

Hey Joseph, did you decide to go with the new Onan 4000i after hearing about the improvements? I'm curious to know if it met your expectations, especially since I'm sure others in your situation would appreciate your insights!