Drive it. Enjoy it. Use it and don't worry about the mileage. MY 90 YEAR OLD MOTHER HAS A CENTRAL AIR CONDITIONER IN HER HOUSE.She sits and sweats because she doesn't want to pay for the electricity. You bought the RV. Use it. You get great mileage if it sits on the drive way but it ain't that much fun camping on the driveway! No one has ever seen a hearse pulling a u-haul. You can't take it with you.
Plug in different values and estimate how many HP it takes to move that rig, delivered to the wheel.
Then work backwards to see if it is plausible for that much energy to be extracted from a gallon of gas.
Off hand, without knowing the details, here is what I would say:
- very slow 45mph or less (low drag) and very good drag coeff (.3 or so)
- level or slight downhill, maybe a tail wind
- minimum weight (empty or nearly so, no toad)
- then a bit of cheating (overfill at start, slight underfill at stop)
- engine / drive train in top condition, very low gearing to keep RPMs down
- tires at max or overinflated.
Unless I'm missing it ... the above does not take into account the biggest gorilla-in-the-room with respect to internal combustion engine powered vehicles' gas mileage ... which of course includes Class C motorhomes.
That gorilla is engine efficiency at converting potential energy in it's fuel into energy delivered to the drive line.
For example I seriously doubt that a 1988 big-block Ford V8 is as efficient at doing this as a 2008 Ford V10. Hence whatever engine you have in your Class C, you might want to take the few little steps that might make it a little more efficient than the engine was/is as delivered by it's manufacturer ... in addition to the factors mentioned in the post quoted above.
(I believe that internal combustion engine efficiences fall somewhere into only the 35% to 45% range ?? Every little bit one can do to improve this will also help fuel mileage.)
I get avg.12.8 with the same eng.and a 31 ft.fourwinds.some times 8mpg. some times 13-14 mpg.I avg.out a 2000 mile trip,got 12.8 which i'm happy with. Ed.
I see your from FL. No one there drives over 45.
Sorry I can not beleave anyone getting anything over 10 MPG AVG.
Traveling in the hills and flat lands best I can get is 8 to 9.5 and very very seldom over 9.
Tom & Bonnie
Aspect 29H 2008 Type C
Ford Flex SEL 2010 There is no B+