Sudden drop in life-of-vehicle mileage

I purchased a Gen4 touring model about a year ago. It has 7000 miles on it.

My aggregate mileage, the number that shows up when you see your total miles on the display, until three days ago was about 53.5. Now, in a single 12-mile trip with normal mileage, it has dropped to 49.5.

Clearly, the way it calculates has changed, suddenly, for no apparent reason. Does anyone have an idea what is going on here?

Another observation: Although the displayed mileage tends to run around 53, the observed mileage runs around 50, so it seems like the meter has suddenly become more honest. But it is still a mystery.

I drive the same route to work every working day. It is about a mile of surface roads, followed by 10 miles of freeway, and ending with another mile of surface roads. When I arrive at work, I can use EV mode for about half a mile, which always makes my numbers better.

I drive 65 to 67 on the freeway, and around 35 on the surface roads. I think I'm keeping fairly steady speeds. Shouldn't I be doing better? (topping the tires up to 40 lbs doesn't change much).

Thanks

 

No, it's my third. Gen2, Gen3, and now Gen4.

 

Mendel: Bingo. That's the weird part. It should be really hard to budge that aggregate mileage figure, almost impossible to make it move 3 mpg in a single 12-mile trip. Something squirrely is going on.

I see you drive a 2010. The 2017s have a number that reports the total mileage over the life of the car. My 2011 didn't have that.

Also, I presume it keeps data in some sort of nonvolutile memory. Does it really reset its stats to 0 if you have to replace the 12v battery?

As for it BSing, yes, but the BS is consistent. My measured mileage (until yesterday) has been about 6% better than my observed mileage.

Bisco: Observed vs. measured mileage. If I go 300 miles, it says I got 53 mpg but I put in 6 gallons, my measured MPG is 53 but my observed MPG is 50. Since this delta is persistent over time, I don't believe it is due to different fill levels; otherwise just as often my observed mileage would be greater than my measured mileage. Settings: I stay almost exclusively in Normal mode. Once in a blue moon I use Pwr Mode for a few seconds. Winter gas: I get better mileage on the summer formula, but the delta in measurements remains consistent. The gas stations won't tell me when they change, but I get better mileage in May than I do in February. It's warmer then too. The delta remains consistent across all these variables.

 

Hi everyone: It is the average mileage over 7000 miles that changed suddenly, from about 53 to about 50. I've tried to be really clear about this.

This car has 4 mileage meters:
Miles since the car was built
Trip 1
Trip 2
Miles since last time car was turned off.

It was the miles since the car was built (7000) that changed abruptly, which is statistically impossible unless something malfunctioned. I did not accidentally reset one of the trip meters. They are both collecting mileage since my last fillup. As far as I know there is no way to reset the Miles Since the Car Was Built. That should be the whole point of such a meter; like total miles travelled, it should collect everything without being reset.

 

In the Gen3, 50 indicated, 47 observed. In the Gen4, 53 indicated, 50 observed (rounded a bit but not much). I'm hoping that it will improve when it's broken in and we shift to the summer fuel. The Gen3's mileage decreased significantly when I changed the tires, and it didn't come back after 1k miles. They were supposed to be similar, according to the Toyota dealer.

 

Got me. However I did not reset it.
How is that different from Trip A or Trip B if they both show the mileage since the last reset? (according to the table, it doesn't show miles since the last reset, but apparently it shows mileage).

 

I did a heap of research, and it all said that the tires I bought were among the best mileage tires I could buy.