RE: Re: How loud are these?
They're screamers.
High RPM, air cooled diesel, un-ducted fan and no sound house=hammering loud.
Noise is why they're being retired to make room for the "tactical quiet" sets. They're still very capable sets.
If it's going to see a lot of use, consider making up a couple of sheets of plywood with an inch of foam insulation glued to them. Put them as close to the gen set as you can without blocking any airflow and cant them with the upper long edge away from the set and towards you. That will help deflect the noise up and away from you. For a "dumb as a rock" fix it works well. Without the insulation, plain plywood is better than nothing.
If it's going to run a lot indoors, consider some other option like it's own well ventilated room. If you need specific ideas for dampening sound or vibration, PM me. I'll send you some drawings for sound dampening wall construction.
We used to run these around the clock with a 2 minute break every 12 hours to check the oil. If you keep the air filter clean, fuel clean and keep up with the oil changes it'll last a long time.
Onan is pretty proud of their parts, price-wise, but everything is available. Three years ago, before I retired, Owl and Saturn used to stock parts. I'd guess they still do.
The generator does not like to be run a long time with little or no load or with an unbalanced load (a lot of power drawn from one leg, little of none from another). If all we were running was computers, we used to plug in a couple of AC units or electric heater on each phase (3 phase) or each leg (240,V, single phase) to keep them from breaking down.
Whether you stick it on a trailer or use it stationary, the Aux Fuel pump will pump from a remote source that's not too much higher than the pump. (Think 55 gal. barrel, deuce or 5 ton tank or 5 gallon jerry can) Real ahndy for long term operation.
Enjoy the new addition to your family.
Lance