We have a diesel generator on our motorhome. The generator uses the same fuel and same tank as what runs the motor. How much fuel will the generator use, let’s say, in an hour? How can I figure out my gas mileage when using the generator once in awhile? —Janice F.
When the generator and the coach engine share the same fuel supply, typically the draw tube (dip tube) for the generator ends at about the one-quarter level in the fuel container to prevent the generator from running the tank empty, leaving you stranded.
How much fuel the generator consumes depends on the size generator you have, how long (in hours) it runs and at what load. The heavier the load, the more fuel consumed. Most makers of generators will publish a guideline of sorts that will estimate the gallons-per-hour rate at a certain load. Once you have that estimate, calculate the number of hours the generator is used on each full tank of fuel and simply deduct that amount from your fuel mileage calculation. The result will probably be close enough, all things considered.