What Is Needed To Replace A Onan QG 4000 With A QG 4000i In A Thor Freedom Elite FE27?
Updated 09/09/2026 | Published 08/06/2025
Question:
I currently have a Thor Freedom Elite FE27 motorhome. Since day one I haven’t had a reliable generator. I don’t want to bore you with the gory details but I have pulled the generator twice. So my question to you is I have a Onan 4000 and would like to retrofit the Onan 4000i into its compartment, besides the generator what will I need to complete the upgrade? Thank you Joe
asked by: Joseph C
Expert Reply:
Hi Joseph!
The Cummins Onan QG 4000i Onboard RV Generator w/ Inverter - 4,000 Watts - Gasoline - CARB Compliant # CM42ZR is almost an exact swap for your current QG 4000. The physical dimensions are the same, but the air intake and exhaust ports are mirrored (see the included picture as it shows that better than I explained it). As long as you can make that work, you won't need anything else to make the swap!
You aren't the first person I have had ask about this swap (it was a different RV though), so I am fairly versed on it. Are you going to be doing this swap yourself or having a shop do it? If you did the work the last two times (sorry to hear that happened), this really wouldn't be any different. Might actually be a little easier as the QG 4000i is a little over 20 pounds lighter!
(click to enlarge)
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on Generators
Joseph C.
8/6/2025
Yes, I have done all the labor. Being lighter would be nice. I’ve been chasing a ghost with my Onan 4000. The first issue was a fuel pump, no big deal. It was fairly trouble free for 40 hours then it quit. It was trouble shot to the control box (too bad everything is jammed into that piece of magic) Replaced the control box and all was well again. The RV went into storage and when it came out it wouldn’t start. It wasn’t sensing voltage out, I probed the plug and had an open on the slip rings. So I pulled the generator and gained access to the brushes. One of the brush leads was chewed through by a critter. Deeper examination there was a mouse house in the generator. I cleaned it up, and tested all the windings, all tested good. I tested every wire in the harness for continuity and for chewing damage. Put new brushes in and closed it up and installed back in the RV. it again was a no start. I was getting intermittent readings on the rotor. I was just there! So out the generator came for the second time and I found one of the new brushes wasn’t in full contact with the slip ring (the curve was different than the slip ring) , so I swapped it out with a brush that was arced to the slip ring. I cleaned the slip rings up and put it back together and back in the RV. During the install I noticed a burned spot in the control board. It was under warranty and was returned repaired. I installed the the control box and started the generator. It ran for about three minutes under load became unstable and stopped. The blink code points back to the brushes, slip rings or windings. That’s where I am now. I just want a dependable generator. There must be hidden damage in the windings, damaged insulation from the rodent occupants that I don’t see. So it brings me to wanting to replace the whole generator with the Onan 4000i. It looks like the hook ups are all doable. The exhaust pipe might take a little adjustment. I looks like the cradle mount that I have will work. About the only rework is the vented door over the generator, I’ll have to move it to the right on the door. One question I have will the existing remote Onan panel in the coach work with the 4000i?