Prius prime mpg fully stuffed + skybox 44-42 mpg highway

EPA is below 60mph,
Add a brick and high speeds your result is expected.

Might consider mounting the box off a trailer hitch and MPGs would improve

 

Only??

At that speed, that is better than an unloaded Gen3 Liftback can do with no roof rack, no external cargo box. It is great that a Prime can get such results with all these fuel-sucking impediments.
Updated MPG vs MPH chart | PriusChat

 

First, you did have power in your battery - it is never below 20% - it just doesn't show up on the dash info. Charge ranges from 20% to 80%, for the reliability of the battery, so you very likely had at least the normal HV hybrid battery power available like all Prius hybrids have always had. That helps to eek out a few more MPG's (though probably not at 85 mph).

Second, only low 40's? Really? You sound disappointed. That actually is stunning with totally ruining the Prime's 0.26 drag coefficient with that box on top, and at those highway speeds you were doing, and fully loaded, and with the air on. You could only get less with high headwinds, all uphill and below 25 degrees or higher than 85 degrees and a trailer hitch and bikes on the back. A normal gas car would struggle to get 18 mpg.

Drive it with no box, one person, slightly better battery SOC, and below 68 mph, and see if you can't achieve the 64 mpg I've been able to get on a tank, and gas only. The car can do it if you don't push the limits.

 

44-42 mpg, with a luggage box on the roof, at 80 Mph? That's amazing! In similar conditions,except the season (summer) my Gen 3 consumption were around 37 mpg . Believe me, yours is an excellent result..

 

No, you wouldn't because the situation and combo is too rare. And mostly, even if there was a duplicate situation, you'd only hear about it here, as we did, from you. Be proud you have the car you do and hopes that you can let your Prime stretch its wings and show what it can really do w/o the cargo box on rural roads in HV mode. And also continuously in EV mode too. Drive happy.

 

You know, with my Gen 3 what surprised me was the fact that at low speeds (30-45 mph) the fuel consumption of the car with the roof box where actually better than without it... I believe that the reason was that the additional load due to the cargo box drag resistance provoked the intervention of ICE, while normally at such low speeds HSD tends to set EV mode quickly depleting the small traction battery.

 

I just recently calculated 104 mpg for the last 721 miles. mph 55 with CC and 2000 foot mountains.

 

How much of that was EV miles? Either way, that's incredible with mountainous driving. As you have no doubt figured out, the mileage drop-off with higher average speeds is fairly dramatic. Remember the oil crisis of the 70's? When they lowered the speed limits to 55, they knew a thing or two about drag and efficiency.

 

I sort of adopted the double nickel as my driving style on the freeway. Here in Ca it’s gotten really bad, speeding, following too close, constant lane change from #1to #3 then back to #1, It’s crazy. Even the Tractor trailers don’t abide by 55 Mph, that’s the law. Cops enforce almost nothing.
To answer your question, I didn’t keep track of EV miles, I know it’s good as my trip consist of mostly EV.
Driving mode is Eco/EV.
On trips I’ll take it up to the speed limit.
Overall I have decided to drive much more defensively and let all the schmucks kill themselves.
Many people don’t even look when entering the freeway, some of those think they have right of way!
I just pull behind the interloper and the autoCC slows me down as well as the other traffic wanting to enter the freeway, the cognizant ones. Much less mental strain and tension that way.

 

The trip odometer thingy has seven readouts. One of them is EV vs. gas miles ratio. Helpful, kinda, if you believe the car is not lying to you.

 

Every time one schmuck kills himself on the road, it seems another gets his license!