Explain this
I have a '11 GMC Sierra 2500 gas. I traded a '09 KZ Spree 261RKS loaded weighed in at 5500 lbs. If I held my speed at 60 I could keep my mileage at 9mpg. Anything over 60 and I would drop to mid 8'...
Forum Discussion
Jayco-noslide wrote:
My guess is that going down does not cancel up because the motor is still running and using some fuel?
Modern gas (and I assume diesel) engines do not use fuel when engine braking. It's easy enough with computer controlled injectors to not inject any fuel when the RPM is well above idle and the gas pedal is not depressed at all.
Fuel mileage up and down hills should be a bit lower than on the flat because you generally use some braking (of some sort) on the downhill sides, so the energy you put in going up the hill is wasted in braking going down the hill. If you don't brake but use the momentum to go up the next hill, it's a lot closer to even.
Sometimes the difference between hills and flats is not as marked as one would think because the average speed in the hills is lower, and so the air resistance is lower and less energy overall is required for the drive. Slowing down in flat terrain would often result in better mileage, too, up to a point.
