Bad Gas mileage - 12v battery solution

NewI have been dealing with mileage dropping over the last 4 months. At 100k, I decided to do some maintenance and with the help of NutzaboutBolts, I went ahead and performed:
1) transmission oil change
2)engine oil change
3) spark plug replacement
4) install oil catch can
5) removeand clean egr valve amd tube
6) remove and clean intake manifold
7) remove and clean throttle body
8) replaced O2 sensor
9) replaced MAF sensor

All of this was proactive maintenance. I had zero issues and no check engine lights.

After all of this, I experienced a slow decrease in MPG- from normal of 50-54 to 44-47.

No matter what I did, light on the accelerator, tires at 40psi, premium fuel, ECO Mode, and overall conscious driving g habits, I couldn't get this thing back to "normal."

Today I decided to bite the bullet and buy a new 12v battery. I had no reason to suspect this was the issue because I purchased this Prius used 2 years ago and when I looked at the battery 2 months ago, the sticker on it said 8/17. I figured the battery is 2 years old- still good right?

Last week, while sitting in my car watching my in-dash dvd player (which came with the vehicle) a message appeared that I had not seen in the past. I typically sit in my car for an hour or a little more, 3 days a week while my daughter has soccer practice. I'll usually pop a dvd in and watch it.

The message said something to the effect- shutting down to conserve battery. I am always in Accessory Mode when watching the dvd.

Today I swapped out the 12v battery with a new yellow top Optima at a cost of approximately $230 dollars at local AutoZone. Drove it right after on the highway for about 10 miles and I'm up over 54!!!

Hopefully, problem solved

 

Stay in Ready to consume electricity, it is much safer.

 

In other words, with the car fully "on", the engine cycling on/off as necessary. Still, doing that won't help the mpg: just switch it right off, bring along a Walkman or similar? Or a book?

 

Or cellphone and unlimited data plan LOL

 

well done! how many miles on her?

 

(silly question, admin delete)

 

Toyota also told me my battery is in great shape. My mpg not so amazing too. Not sure which battery they were referring to; I always assumed it was the hybrid - now I'm starting to think it was the 12V, not that they were spot on or anything. They gave me this small piece of paper with 4/5 dots full kinda like a tiny receipt.

Karl thanks for stopping to write details such as the remote not working and whatnot. From what I read around here I might have the same issue.

 

that is definitely a 12v report. is it original?

 

What type of tires do you have on the car now?
I will never get the cooper tires again. I'm going back to the Continentals. It's just too hard to get
the MPG's up. I've lost 5 mpg with the cooper tires.
For "ME", tire pressure only gained me possibly 1 mpg.

I seem to remember you asking about tires, did you get new ones yet? If so, which ones did you get?
That could be where you are loosing the mpg's.

 

I got 4 set of Continental Wintercontact SI Plus about a month ago.

 

Winter tires... okay. From my understanding of what others have said on Prius Chat, you'll loose the mpg's
with winter tires. I guess it's how they are designed for the snow. You may have to live with them until summer.

 

Maybe. Time will tell. Gonna check that battery for sure.

 

Yep, doesn't hurt to check the battery. Check everything and get everything repaired and up to date.
Then you eliminate each item and can narrow things down to find a cause to a problem.

 

I'm getting better mpg on my 9 year old 15" X-Ice, than my new 17" Primacies...

I'm sure it'll level out in a year or two, but just sayin'.

 

I think the 17” wheel is havier than the 15” - so not only the tyre model, but the wheel size also counts.

 

Yeah definitely, something like 24 pounds vs 16~17? And yeah 17" tires are heavier too. I can feel the difference every time I swap them.

 

I have my summer tyres on 17” and the winters on 16” - from Prius gen 2, 7 kg / ~15 lbs without the tyre. Summer ones are stored on my attic, I can feel your pain.

 

I've found a lifting technique that's easy, and easy on the back:

Bring the wheel/tire up close, oriented roughly correct. Sit on the floor facing it, hook your toes under the wheel at around 5 and 7 o'clock. Lift the wheel with your toes while steadying and guiding it with your hands, onto the lugs. Helps to have good light, so you can see the studs through the wheel holes, line them up.

 

my technique since decades /

 

Thanks for sharing Karl.

I had a very similar experience. The car had good imperial mileage 56mpg but sometimes the doors weren't unlocked after I pressed the remote and I had to try it a few times.

Then a week after a 300 miles drive, my car wouldn't start and I had to jump start it.

After that the remote never failed again, but the mpg I get now is around 38mpg.

I will definitely take it to a mechanic for them to replace the 12v battery, didn't even realise it was this but it will most likely be the culprit of the extra fuel consumption.