Why did my mpg drop suddenly today?

[dominicsavio]

Folks,
I am in suburban philadelphia where it's been a nice and warm summer over the last couple of months - enough for me to average ~57 mpg over the last 2 months.

Driving today (normal temp - 85F), my mpg dropped to 52, then the charge on my hybrid battery went down to a total of just bars and as I continued driving, the charged picked up but mpg dropped to 45.

I've never seen this happen so am wondering what people's thoughts are on this.

Is there a problem with the hybrid battery? How can I tell? That's the only thing I can think of....

One (minor?) thing: I also accidently pressed the RESET button on the MFD yesterday (before which mpg was ~58) - pretty sure this has nothing to do with it but you never know!

Thanks all..

[PaulHS]

Originally Posted by dominicsavio

Folks,
I am in suburban philadelphia where it's been a nice and warm summer over the last couple of months - enough for me to average ~57 mpg over the last 2 months.

Driving today (normal temp - 85F), my mpg dropped to 52, then the charge on my hybrid battery went down to a total of just bars and as I continued driving, the charged picked up but mpg dropped to 45.

...

My first thought is Air Conditioning. Yesterday and today are the first days this year that I've used it. If not set conservatively, A/C can drag your mileage down. Any chance?

[yardman 49]

If you have not pressed the Consumption screen "Reset" for thousands of miles, what you've been seeing for FE has been a running average of the FE for all those thousands of miles.

Now you will see some wild "swings" until your running average grows again.

Just a simple math issue really.

Best wishes,

Frank

[paprius4030]

Since you pressed the reset button it will only show your average with the few miles you have driven since hitting the reset instead of the many miles driven before. This will cause your "average" to flucuate alot more than before.

[dominicsavio]

Thanks all.

So let me also clarify a few things:
1) I always press reset with a new tank of gas
2) For most of today (and also yesterday immediately after pressing RESET, I didnt use the AC although I did use it very briefly on my way home)

I'm obviously hoping it's no big deal but nonetheless have a couple of questions:

1) (a) How do I know whether the hybrid battery is wearing down? - and (b) will it show up in the mpg. I dont know why (and for no particular reason), I have the nagging feeling something may be up with the hybrid battery

(2) What's the best (i.e. most efficient) way to use the AC so as to get max MPG while also using the AC

[ETP]

Originally Posted by dominicsavio

Thanks all.

So let me also clarify a few things:
1) I always press reset with a new tank of gas
2) For most of today (and also yesterday immediately after pressing RESET, I didn't use the AC although I did use it very briefly on my way home)

I'm obviously hoping it's no big deal but nonetheless have a couple of questions:

1) (a) How do I know whether the hybrid battery is wearing down? - and (b) will it show up in the mpg. I don't know why (and for no particular reason), I have the nagging feeling something may be up with the hybrid battery

(2) What's the best (i.e. most efficient) way to use the AC so as to get max MPG while also using the AC

Good question. I took my Civic Hybrid in because the battery went to zero while I was driving it and the mileage went down also for the last 6 months. They said everything was fine and shoved me out the door. Dealers in general do not care unless the vehicle is visibly broke. Tire pressure, oil, AC, tires, electronics, AC on low fan and recirculate.

[krousdb]

Don't worry about it. Your battery is probably fine. Every once in awhile, the Battery ECU needs to recalibrate itself. You will notice unusualy activity during that time. Yes your mileage will drop. I expect your mileage to go back to normal. If not, let us know.

[PaulHS]

Originally Posted by ETP

... Tire pressure, oil, AC, tires, electronics, AC on low fan and recirculate.

In addition to "AC on low fan and recirculate.", set the temp to the highest comfortable temperature.

Have you recently had your Prius serviced by the dealer? As mentioned above by ETP, dealers tend to overfill the oil and reduce the tire pressure. Both of these can negatively affect mpg.

[wfolta]

Speaking of dealers, I've also heard that if the 12v battery is disconnected for some kind of electrical servicing, the ECU resets and has to relearn your driving habits over a couple of weeks.

[dominicsavio]

All this is very helpful.

I have not had my car serviced anytime recently so, at the end of the day, my guess is, the battery just recalibrated itself.

Out of curiosity, why set the AC on recirc (instead of drawing air from outside).

Also, when you are not using the AC and it's nice and cool outside, I suppose you could set the fan to drawing air from outside (without using the AC)?