Gained 3 MPGs after fillup, thinking there's something up with the gas

Could be a different supplier or another configuration in additives. Count your blessings if the mileage went up.

 

I've always wondered if I used 100% gas (no ethanol) if my mileage would go up. I have a Shell station close by that sells it, but it's about $1 higher than reg. gas. Doesn't seem worth for 2-3 mpg more.

 

We don't even get the choice here, it's all 10% ethanol.

 

One thing I noticed that if one day I get worse MPG, lets say 50 MPG, next day it's going to get better, say 60 MPG, delivering the expected 55 MPG average on the MPG indicator. Same commuting routine mind you.

 

I have given up on monitoring mpg, or even m/kWh.

I have started just monitoring the actual fuel usage per commute trip, in each direction, using torque.

 

You are just monitoring zeros then. You don't use any fuel.

 

I was driving the Prius over winter break while my son drove "his" Volt. I followed another Prius to a gas station.

 

3 miles difference at 55 miles per gallon is some 5% difference. That's a small amount of gas. The error in your calculations could be that much. Even different pumps at the same station could give off that much error. Temps in northern ca were a few degrees warmer the past week.

 

I noticed something similar last summer, where the mpg in both of our cars dropped by about 4 mpg at around the same time.

A drop in one car is one thing, but a drop in both cars during the same period, using gas from the same company/location is pretty strong evidence I would say.

Both cars were monitored on Fuelly.

 

Strong evidence for sure. But you'd need additional data points to be conclusive. What was the fuel economy for the next tank?

 

Direct links to the mpg info on Fuelly: Camry, Prius

OK, now that I look at the graphs for mpg for both cars side by side, the mileage drop was not at the same time, and the drop was 3 mpg not 4 mpg.

However, it is interesting that both vehicles showed a pretty noticeable drop in mpg followed by a recovery to average mpg. The graphs are eerily similar, the difference in time might be due to the fact that the Prius is fueled half as often as the Camry, so the drop in mpg shows up later for the Prius.

 

Another thing to keep in mind is that the pump can shut off at a different spot from time to time. My old 95 Neon was all over the place on high way mpg and when the evac system messed up and I bypassed it...only allowing it to be filled up at a VERY slow pace...now every fill up goes to where it is near the top and I can hear it getting ready to pour out, but then it will click off. At 55 mph I always get 46 mpg, 60 mph it drops to 42-43 and 40 at 65. All those speeds are when I am slip streaming off of semis...at a SAFE distance.

 

Yeah, quality (energy content) of gasoline can definitely vary from place to place at the same time of year.

Early last fall on a trip from Dallas to Santa Fe NM we filled up twice, averaged a terrible 43-45 mpg (real miles divided by real gallons). The gasoline back here in good old NM gave us our usual 50-52 mpg until cold weather set in. Same brand (Shell) both places and same time of year - has to be different fuel quality.

 

Don't you guys have different summer and winter gas there? We do in California, when switched to winter blend we gain power so MPG goes up.