2010 Prius II, tire pressure 3 PSI over door sticker, new car with 440 total car miles at end of trip. Used cruise control at 65 mph most of the time. All data is read directly or calculated from the Prius instrumentation readouts. My wife and I decided to drive from Lincoln California to Truckee California for ice cream cones. I topped off the gas in Lincoln at 180 feet elevation and headed to Truckee on I-80 after about 7 miles on CA-65. At Donner summit, 7221 ft elevation and 79 miles our trip fuel consumption was 35.2 MPG, after we dropped down into Truckee at 5230 feet elevation and 88.3 miles from home, trip fuel consumption was 38.7 MPG. The ice cream cones were good. After we got back to our home in Lincoln at 350 feet elevation, our average fuel consumption was 51.3 MPG. After doing some calculations, the Lincoln to Truckee MPG was found to be 38.7 MPG and the Truckee to Lincoln MPG was 80.8.
You will find even the slightest elevation change (that looks flat when you are driving) will make the MPG go from 80mpg+ downhill and 20-30mpg uphill. You will be able to spot the terrain's slope by the mpg readout and the pedal pressure soon enough.
My rule of thumb is that climbing requires roughly an extra 1 gallon per 10,000 feet, compared to the same distance of flat road. This figure will vary depending on the Prius's load. A similar amount of fuel should be saved on the descent if it is shallow enough to not require friction or engine compression braking. On your ice cream run, appears to have come close to this rule, needing 1 extra gallon per 8500 feet of climb. Did you have a little bit of friction braking or B-mode descent? If not, my rule is a bit further off than I expected.
There was a fair amount of engine braking on the Donner Summit to Truckee stretch and the Donner summit to Lincoln stretch. It sounds like you used the Donner summit elevation instead of the lower Truckee elevation as the high end. Whichever you did, it's nice meeting someone who considers and calculates fuel to change elevation:yo: I figured 1 gal/6700 feet using 3600 lb GVW and 0.3 efficiency gas tank to road efficiency using 10% ethanol corn lobby debilitated gasoline
So this sorta follows along with your experience. When I lived in Lincoln (off 5th st.), I would commute to Sierra College via Hwy 193 and Sierra College Blvd.. I would average 53mpg during those trips or just about any flatland driving. When I started commuting to Auburn for work my MPG would drop to 48mpg avg. due to the elevation change (164ft. to 1,200ft.). Even if I coasted down Hwy 193 (Auburn to Lincoln) for most of its length, I could never recover the mpg lost going up it (Lincoln to Auburn).
