Replacement For Older Onan QD 12500 Diesel RV Generator
Published 10/30/2026
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Question:
I have an older Onan Quiet Diesel 12500 generator in my diesel motorhome that's getting expensive to repair. I'm thinking about replacing it instead of putting more money into it. Do you have a newer version of the QD 12500 that would work as a replacement, or would I need to make major modifications to the generator compartment?
asked by: Robert E
Expert Reply:
Hey Robert! I recommend the Cummins Onan QD 12500 Diesel Generator # CM74RR to replace your older unit. This is the newer version of the QD 12500 with the same 12,500W output, and it's designed with similar dimensions and mounting locations to the older models.
The generator measures 41-3/8" long, 24-1/2" wide, and 27" tall. The intake, exhaust, and drain locations are also similar to the older QD 12500 models, so you typically won't need major modifications to your generator compartment. You'll still need to reconnect the fuel lines, exhaust, and electrical system during installation.
You can also upgrade your setup with the Cummins Onan EC-AGS+ Automatic Generator Start System # CM58GR. This lets your generator start automatically based on battery voltage or temperature, which is especially handy when you're away from your motorhome.
What motorhome do you have, and how long has your current Onan been in service?
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Product Page this Question was Asked From
Onan Generator - Quiet Series Onboard RV Generator - 12,500 Watts - Diesel
- Generators
- No Inverter
- Diesel
- 4001 Watts or More
- Onboard Generator
- 120V Output
- 240V Output
- Carbureted
- Electric Start
- Cummins Onan
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Robert
10/30/2026
I have a 2012 Tiffin Allegro Bus, and the generator is original, so it's about 14 years old. It's still running, but the repair bills are adding up. I'm glad to hear the newer model is similar since I really don't want to modify the compartment.