If I may jump in here:
Rule of thumb for diesel generators.-- 13 KWHr per gallon with a reasonable load.
Fuel consumption specs and comparisons.
Your actual consumption will depend on the Specific Gravity of the fuel. The relationship is quite linear.
If you see a set with noticeably less fuel consumption than the competition, read the fine print and check the SG of the test fuel.
At least one manufacturer has posted consumption specs showing about 10% less consumption than the competition. They were testing with fuel that was about 10% heavier than the fuel used by others.
Read the fine print!
Bill
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"Why not the best?"
Jimmy Carter