Author Topic: Prius mileage plummeted  (Read 1029 times)

Travis

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Prius mileage plummeted
« on: July 22, 2017, 09:59:15 PM »
I've been driving my 2008 Prius for two years and I get 45-48mpg consistently.  It drops to the low 40s during winter, but besides that I've had no major hiccups.  I had an oil change and tire rotation 3 weeks ago. I drove from Sacramento to Phoenix with no drop in fuel economy. A couple weeks ago upon arrival here in Arizona I filled up the tank and as soon as we left the gas station my mileage dropped to the mid-30s.  I'm near the end of that tank and I'm holding at 37mpg with a mixture of city and highway driving.  Any ideas what might have caused the drop?  With the high heat I assume it's not the tire pressure, and I haven't noticed any changes to the car.  If this next tank of gas does the same thing I was going to take it into a Toyota dealership, but I wanted to run it past you all first.

Thinkum

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Re: Prius mileage plummeted
« Reply #1 on: July 22, 2017, 10:19:09 PM »
If I remember correctly, that is a sign your hybrid battery is going bad. Have you asked or poked around on Prius chat? I replaced my battery in Gen II and while I didn't get 37, I did dip down to 40mpg or so. Then I noticed it was not charging up as quickly. If you go onto Prius chat, there is a FAQ and you can run a simple diagnostic yourself using the cars display to show the life of the battery. Good luck.

WSUCoug1994

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Re: Prius mileage plummeted
« Reply #2 on: July 24, 2017, 01:53:03 PM »
Does the increase in AC use have an impact? 

trammatic

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Re: Prius mileage plummeted
« Reply #3 on: July 25, 2017, 12:07:59 PM »
Could you accidentally have filled up on a higher-percentage ethanol fuel?  E-85 or E-100 will get significantly worse fuel economy.  I'd try a different station next time and see if it recovers.

dandarc

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Re: Prius mileage plummeted
« Reply #4 on: July 25, 2017, 01:09:20 PM »
Could you accidentally have filled up on a higher-percentage ethanol fuel?  E-85 or E-100 will get significantly worse fuel economy.  I'd try a different station next time and see if it recovers.
Hoping it is this for you OP.

This guy did this on purpose, and saw a pretty big drop in fuel economy:
https://sorrywv.wordpress.com/2012/04/28/can-i-use-e85-in-my-prius/
Link to my journal, so I can find it quickly - http://forum.mrmoneymustache.com/journals/dandarc's-journal/

Travis

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Re: Prius mileage plummeted
« Reply #5 on: July 25, 2017, 03:27:14 PM »
As far as I know it was just a random Shell station and I filled up with the usual 87.  I just filled up again a couple hours ago at Sam's Club so we'll see how it goes for the next week or so.  I went to PriusChat and they have a DIY test for the 12v battery.  I'm going to try it out tonight and I'll let you know what happens. It looks like I'm still on the original battery so it might be starting to wear out.

https://priuschat.com/threads/weird-stuff-happening-mpgs-dropping-test-the-battery.73400/

kevj1085

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Re: Prius mileage plummeted
« Reply #6 on: July 30, 2017, 04:37:29 AM »
If it helps any, for years living out here in az I've dropped performance in mine in the summer months and increased it again in the winter months. I think it's the heat. I read something about how the car does everything it can to protect the hybrid battery so in extreme heat it won't kick on until it's cooled down sufficiently. In city driving w all the stop lights I've been getting 34-38mpg. Just yesterday we drove 18 miles to and from the zoo on the highway, weather was 90ish, and I averaged 61 mpg on the way there and 50 on the way back. I've had it for 10 years.

ShoulderThingThatGoesUp

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Re: Prius mileage plummeted
« Reply #7 on: July 30, 2017, 04:46:02 AM »
If it goes back to normal it's probably the car protecting the battery from heat. I know my C-Max Energi insisted on using gas right after a charge on a really hot day (for Pennsylvania) once.

Does your Prius have mode buttons by any chance? Any possibility you switched it to something like a Comfort mode that would have decreased regen?

GuitarStv

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Re: Prius mileage plummeted
« Reply #8 on: July 30, 2017, 06:08:45 AM »
I know you said you're assuming that it's not tire pressure . . . but have you checked the tire pressure?

Travis

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Re: Prius mileage plummeted
« Reply #9 on: July 30, 2017, 12:44:29 PM »
I had the tire pressure checked a few minutes ago. The shop put about a pound into each tire, but on the way home I didn't see any noticeable increase. I also ran that battery test and it came back good.  I didn't think it could be too hot for the battery system, but it's certainly possible. I've never had the car in a 100+ environment until this month.  Even during vacation in CA last month I only drove it in those kinds of conditions on a couple days.  The battery vent in the passenger area has been blasting quite a bit since we moved here.  My average right now is 37.  When I'm driving very slow or right after I first start it up it stays at 20 or below for a couple minutes. On the straight-aways or on the highway it might jump to the low 40s, but not enough to raise the average.

Travis

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Re: Prius mileage plummeted
« Reply #10 on: August 04, 2017, 04:55:47 PM »
If it helps any, for years living out here in az I've dropped performance in mine in the summer months and increased it again in the winter months. I think it's the heat. I read something about how the car does everything it can to protect the hybrid battery so in extreme heat it won't kick on until it's cooled down sufficiently. In city driving w all the stop lights I've been getting 34-38mpg. Just yesterday we drove 18 miles to and from the zoo on the highway, weather was 90ish, and I averaged 61 mpg on the way there and 50 on the way back. I've had it for 10 years.

The consensus at PriusChat is that the extreme heat is stressing the A/C, engine, and battery.  The fact that my car is 9 years old and still on the original 12v battery might be a factor too even though it is charging properly.  We'll see how it looks over the next few months. Thankfully my commute is only about 10 minutes so it's not a great loss of money in fuel.

DavidAnnArbor

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Re: Prius mileage plummeted
« Reply #11 on: August 04, 2017, 05:38:04 PM »
Also, sometimes in high heat, the gas tank may expand and you actually filled up more gasoline in the tank than normal.