Gas Mileage Discrepancy Prius IV

[john burns]

I took my 1st long trip in my new Prius today

I took rte 95 from northern FL, and traveled south to New Symrna, for a distance of 150 miles. Set cruise control at 65, stayed in right land had no traffic. Gas mileage was 55.2 MPG.

I did the same on the return trip going north. Again no traffic, used cruise control set at 65, and watched the MPG deteriate. Eventually hit 53.6 MPG

Both ways there was no traffic and I drove cautiously to not have to decel and then acel back to 65

Any ideas as to why the difference?

John

[qbee42]

That's so close as to be statistically insignificant. Even if the difference is real, any number of factors could cause such a small shift: terrain, wind, road surface, traffic, temperature. I wouldn't worry about it.

Tom

[georgew]

I'm not sure how you're calculating your mpg but it seems that the onboard display is at best an estimate and can't be relied on for accuracy.

The thread below has more information.

2010 Toyota Prius FCD Inaccuracy

[PriusRos]

Originally Posted by john burns

I took my 1st long trip in my new Prius today

I took rte 95 from northern FL, and traveled south to New Symrna, for a distance of 150 miles. Set cruise control at 65, stayed in right land had no traffic. Gas mileage was 55.2 MPG.

I did the same on the return trip going north. Again no traffic, used cruise control set at 65, and watched the MPG deteriate. Eventually hit 53.6 MPG

Both ways there was no traffic and I drove cautiously to not have to decel and then acel back to 65

Any ideas as to why the difference?

John

Did you reset the odometer at the beginning of each trip? (if the odometer was not reset, your return trip would actually be lower than 53.6 to have brought down the average.)

Even if its lower than 53.6, I agree that the difference is so small that it is probably not significant. However, one thing that could make quite a difference, everything else (weather, speed, traffic, etc.) being equal, is if there are more uphill climbs in one direction than the other. The inclines could be so slight that you don't even know you are going uphill, but the car does. See the thread:
Uphill vs. downhill makes the biggest difference

[macmaster05]

Another mileage discrepancy that you'll find is that your ACTUAL mileage will not match your computer mileage. In most cases, your computer will overestimate it by 3-6%.

I just got back from the gas station 5 minutes ago. My computer read 54.8 mpg. My actual was 51.4.

And that's with a Gen II Prius. Give me a Gen III and I would be able to make magic. I digress.