Dear Gary,
We have a diesel generator on our motorhome. The generator uses the same fuel/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.
Dear Janice,
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; this, to prevent the generator from running the tank empty, rendering 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 all 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. So you have a little homework to do. —Gary Bunzer
##rvt753
I use two methods to calculate a more accurate fuel usage than the generator ‘s manual estimate. I track both miles per gallon when not using the generator (about 8 mpg) and gallons per hour when not driving. I can do the later because I often dry camp in a location where a gas station is nearby. So, I can figure that when doing both, my miles per gallon is probably close to the average, and I can figure how many gallons went to miles and the rest to generator hours, or vice versa, using the average figure for whichever used the least amount of fuel.