Mileage under 40 on cross country trip

Wrong guy........

If you average all of your mileage figures you come out to about 47 mpg. I say not bad for a Prius C (city) that is being driven cross country, on the highway at 75 mph, fully loaded, AC blasting, with high outdoor temperatures. Keep in mind that the vent for the traction battery is in the back of the car near the battery itself. You said the temperature on your last trip was 100 degrees. Remember that ECO mode reduces the output of the air-conditioner, so if you were barely keeping cool up front with the air blowing on you, remembering that the luggage would block cool air from getting to the back of the car even if the vent wasn't blocked directly; your traction battery was probably sweltering. This would kill its ability to provide efficient power. So unless your car keeps giving you low mileage when you get back to regular driving under normal conditions, I would say it is normal. I also strongly recommend doing anything you can to keep your traction battery from overheating at all costs, because it can be damaged by excessive heat.

40 mpg is not bad for that ride. We tow ATV's from NC to Utah and the part through Kansas and the other middle states we normally get 8mpg or so in our pickups. It looks flat but is 500+ miles of uphill.

The AC on Prius's takes alot of power. Hurts mpg but feels good. My Prius II takes a 5mpg hit for AC on 95+ days.

The c isn't optimized for the highway like the regular Prius, higher CD. So 75 mph, 100+ degrees, AC set on 69 and fully loaded, yeh 40 MPG sounds right!

Thanks everyone for the helpful info. I figured all the external factors (luggage, going 75, ac blasting) had an effect but wanted to know if that assumption was correct. Funny enough though, on the final 450 miles of my trip, after filling up the tank, I got near 60 mpg for a good 70 miles before it slowly dropped to 50 mpg. Same amount of luggage, hotter temps. More hills though.

Wind can also have a profound effect on your mileage, a good tailwind can add quite a few MPGs and a headwind will suck it down!

OKC and Albuquerque have a ~4000ft difference in elevation, so you'll loose a couple mpg due to that. My guess is that the majority of the rest is from going into significant headwinds.

In addition to high speed and added weight, poor mpg on this stretch is a combination of two factors - headwind and increasing elevation. We drive from Denver through Albuquerque to Phoenix several time per year and the ever-present headwind kills good mpg. Also, at about mile marker 49 in Western NM (about 30 miles East of Gallup), you will see a "Continental Divide" sign on the side of I-40. This shows that you've been driving uphill for hours, even though the landscape looked flat and featureless.

Dont forget here guys that we just now receiving summer blended fuels all around the US. If you read in your owners manual and on the fuel cap E-10 fuel is the max allowed alcohol content allowed by Toyota. Summer blends tent to have the full 10% content. I just bought my C III on Sunday and I am getting 50mpg already with only 100 miles on it but That is not a great marker really. At 500 miles I will be changing the oil to MB1 0w20 and a new Toyota filter. And I'm going to experiment with 91oct fuel as well to see if the 14.1 compression ratio likes it better.