I have a 7.5 diesel generator and am wondering what the fuel enconomy is?
Does any-body know how much fuel (GPH) they use on an hourly basis?

From here:

http://www.google.com/search?q=onan+generator+diesel+7.5+fuel+usage

I got this page:

http://www.cumminsonan.com/www/pdf/specsheets/a-1390.pdf

It shows these numbers:

no-load .25 GPH
half-load .56 GPH
full-load .90 GPH

Les:

I have the 10K... let me give you the 10K numbers which should give you a pretty good idea (maybe scale down just a little).

The 10K is 0.1gph at no load, 0.6gph at half load, and 1.1gph at full load. I use a rule of thumb that it takes 0.1gph of "overhead" and add 0.1gph for each 10amps I'm using (based on the fact that it puts out 90amps and uses 1.0gph above "overhead" at full load).

So if I'm running at 30amps, I figure it uses about 0.4gph. That's worked out close enough for my use. Again, yours is probably about 20-25% less +/-.

Cheers/Jerry