I recently made a trip to Dallas from Austin and back. Going to Dallas and drivng within Dallas, 264 miles i filled up with 4.5 (top off) gallons before starting return trip that comes out to be 58.66mpg. After coming back to Austin top off again after 228 miles and needed 5.26 gallons which comes out to be 43.35mpg. All this with cruise set to 72mph and 3 people in the car with AC on. I did drive through some stop and go traffic going to Dallas and no traffic on way back as it was late in the night. But that's just too mch of a discrepancy that i can not explain. Any idea why fuel efficiency might be so different on essentially same route going one way then comng back?
If you had a truck that got 10MPG and sometimes it only got 9MPG you wouldn't think much of it... However that would be a far more drastic fluctuation in MPG numbers than what you're experiencing. As in it's totally normal for a Prius to be fluctuating with the MPG range you're describing. There's so many things that can change MPG. And number one reason people get bad MPG on an otherwise fully functional vehicle is tire pressure... Pump those tires up higher than normal and you'll definitely see an MPG improvement.
I'm going to go with: Primary factors: - Your trip from Dallas to Austin(43mpg) was nearly completely at 72mph. You're getting little to no extra benefit from the hybrid system at constant highway speed. - Your trip from Austin to Dallas included around 40 extra miles of city driving around Dallas. You got the full benefit of the hybrid system in that part of the trip. EV driving time, ICE off at stoplights, etc. You also got a mild boost from the slower traffic on the way in. Secondary factors: - You don't know if the two gas pumps filled your tank to the exact same level. The pump in Dallas may have slightly underfilled(inflating your mpg) and/or the pump in Austin may have slightly overfilled. - Wind speeds could have been different. If you had some level of tailwind on the way to Dallas and/or a headwind going to Austin, that could have made a big difference. - Temps could have been different. This is the least likely, but it's possible the climate controls needed more power on the way back(doubtful, but there's a tiny chance) Austin is technically higher in elevation than Dallas, but it's by such a tiny amount(~10') that I can't believe it could be a major factor. Still, the shape of the terrain could have possibly had an impact if any hills in between tended to have steep slopes on one side and gentle slopes on the other. Camper is also correct that a Prius(esp. an LE) is going to see bigger fluctuations than most any other car. A 20% difference in a 20mpg car is 4mpg. The same 20% difference in a 50mpg car is 10mpg.
Agree with replies - in my opinion: - wind is a huge factor. On a road trip, wind at my back I get 55 easily, but headwind it will be in the 40s for sure. - local driving in Dallas will most definitely give you a higher MPG than 72 on the highway, so since you included the local driving in your one-way trip, yes that trip will be higher mpg. - in my opinion, once you get above 68 or so, there is a hit to the MPG, so at 72 cc, you are not at speed to get optimal mpg. 43.x seems low, but if your tire pressure is on the low side, you had a headwind, and was going 72 the whole way, it is reasonable.
I keep an eye on my tire pressure, they are inflated correctly to be over 1psi than what the label.on door jamb says, each. Driving against wind might be true on return trip but will it cost 15mpg!?
Depending on the wind, yes. At 72 mph, 5th gen LE requires ~22 hp. Add a 10 mph headwind and that jumps to ~30 hp. (These are with 150 lb driver; with two more passengers these figures will be slightly higher).
Houston or Austin towards DFW there is always a significant tail wind. Going back down south, it turns into a headwind. I have noticed the same.
