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Discussion Starter #1
Prius friends,
It's been quite some time since I last posted. It's nice to see some familiar names are still around. :)

Over the past few months the average MPG on my Prius has been on a slow decline and I'm wondering if anyone has experienced a similar decrease, or has any ideas as to what might be going on.

Purchased new in October of '03, the car has never averaged less than 40 MPG per tank and typically ranges between 42 and 48 MPG, depending on driving conditions, temperature, etc. My average MPG per tankful has now dropped into the high 30's.

Items of note:
When new the MPG display and physical calculations were within +/- 1 gallon; that difference is now +/- 3.
The gas tank filler neck TSB was performed about a year ago.

I'm taking the car in to be checked later this week, but thought I'd look for some comments and advice here first. Anyone?

TIA,
Moo :)
 

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Hey Moo! Nice to see you back!
I do get a gas drop off this time of year even before the tempreature goes down. I think they change the gas formulation to a winter mix, and I lose about 3-4 mpg. That wouldn't explain all of what you describe, but it may be part of it.
I know it's too obvious to mention, but if the tires are low... never mind. :wink:
 

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I too have noticed a slight (~2 MPG) drop in mileage over the last couple months. I attributed it to the temperture getting a little cooler here. This will be my first "winter" with the car. I figure the batteries operate more efficiently when it's warmer.

Do they use winter formula gas in Southern California?
 

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Air filter dirty

New tires (stickier)

Last oil change ended up too full

Heavier load in the car (don't be offended)

I had a 4 mpg drop and found ONE tire had a slow leak and had dropped to 17 lbs. (WOW)

You changed the ROUTE of your primary commute

Just some random thoughts
 

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Discussion Starter #5
Thanks for the replies. I've checked all the usual suspects (tire pressure, oil level, etc.) and am aware of the seasonal mileage differences. I don't believe this is related to any of those causes. It appears that my MPG is in a slow decline that started in the summer months and is continuing to drop. I'm entering my third year with the Prius now and this is an unprecedented turn of events. I'm curious to see what the service tech can tell me about this when I take it in later this week.

Hey, Hep, thanks for the welcome! I'd show up around here more often, but demands on my time keep me from participating as much as I once did.

Moo :)
 

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moocatdog said:
Thanks for the replies. I've checked all the usual suspects (tire pressure, oil level, etc.) and am aware of the seasonal mileage differences. I don't believe this is related to any of those causes. It appears that my MPG is in a slow decline that started in the summer months and is continuing to drop. I'm entering my third year with the Prius now and this is an unprecedented turn of events. I'm curious to see what the service tech can tell me about this when I take it in later this week.

Hey, Hep, thanks for the welcome! I'd show up around here more often, but demands on my time keep me from participating as much as I once did.

Moo :)
But Moo... something is missing! Where is the "drive happy?" :(
 

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Discussion Starter #8
Ah, yes. I had forgotten about my old sig block. I always thought it was a pretty good one. Thanks for reminding me.

Drive happy,
Moo :)
 

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Here's a possible answer: HV battery charge range declining.
If the battery is starting to get weak, symptoms would include worsening acceleration and MPG.
You probably won't get a DTC for this, as the voltages still fall within range, just not as long as they used to.
If you have an EV mod, see how far you can drive at 34MPH starting at 6 bars before it kicks out of EV and ICE starts.

Maybe we should all do this to get a baseline so we can tell when the HV is starting to go.
 

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DanMan32 said:
Here's a possible answer: HV battery charge range declining.
If the battery is starting to get weak, symptoms would include worsening acceleration and MPG.
You probably won't get a DTC for this, as the voltages still fall within range, just not as long as they used to.
If you have an EV mod, see how far you can drive at 34MPH starting at 6 bars before it kicks out of EV and ICE starts.

Maybe we should all do this to get a baseline so we can tell when the HV is starting to go.
Just out of curiosity, would using the EV switch cause you to have more drastic drain/charge cycles and could that reduce the battery life?
 

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I doubt you could use the EV enough to do harm. Remember, the car limits the actual SOC range used, and this is not changed with EV. You can't do worse than being in park often with the AC running.
 

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Discussion Starter #13
Dan,
I don't have an EV mod, so I can't test as you described. Is there a history of batteries weakening? I've not heard of this before. Aside from lower MPG, I've not noticed any perfomance issues, such as decreased acceleration.
Drive happy,
Moo :)
 

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Paulie said:
mikepaul said:
Techron-based fuel line/fuel injector cleaner?...
Just a general question to anyone: What is Techron? Here's the MDS sheet, I can't find what is special about "Techron" or what it is (Stoddard solvent???)

http://householdproducts.nlm.nih.gov/cg ... id=3012002
Techron™, is some random additive Chevron produces. The joy about made-up, trademarked names, is you don't have to prove it does anything at all. "Now, new Moosville brand cow's milk, with more Moorevin™!"
 

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ehurtley said:
Techron™, is some random additive Chevron produces. The joy about made-up, trademarked names, is you don't have to prove it does anything at all. "Now, new Moosville brand cow's milk, with more Moorevin™!"
Ah, I understand. It's like the "Intel Centrino Technology." There isn't really anything "Centrino" except for a combination of a Pentium M, a wireless card and chipset. Change anything to a different part (like an IBM wireless card instead of an Intel one) and it's not "Centrino" anymore, because that's what the marketing department says so. :)
 

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Ah, but they do claim something: keeps the engine clean so it runs in top shape.

Centrino just claims reliability, since it is certified to work together.


Naptha, isn't that the ingredient in moth balls?
 

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mpg drop

:kiss:You bet I've experienced this. I have a 2006 and the change seemed sudden to me. My average has been 43 mpg since I purchased the car new. Now I'm lucky if I can get 40. It's summertime and VERY HOT where I live. (I know about winter gas also - has made a little difference sometimes.) My dealer told me, and from comments here, sounds like it wasn't just blowin' smoke: The battery gets older every year. When it is exceptionally hot and the A/C is blowing like crazy, the battery has to work harder and harder. I couldn't find out if it is an indication of soon-to-be battery death, but would sure like to know since I have 100,000 miles on mine and would rather buy a new Prius before the $3K battery gives out than after. What did your mechanic/dealer tell you?
 

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We replaced the traction battery last summer. Luckily, Toyota and our dealer's service department absorbed part of the cost; and our net, out-of-pocket expense was only about $850.

While even $3,000 is a lot of money, it's only a few new car payments. If the rest of your Prius is in good shape, I'd just wait and replace the traction battery when it fails. That's what we did, and our 2002 is still going strong!

Good luck!

Note: Check your tire pressure. If the "max pressure" printed on the sidewalls is 44 psi, pump the tires up to 44/42 or 44/40 psi (front/rear). Your mileage will increase 2-4 mpg. I have to check our tires every time we take our Prius in for routine preventative maintenance, because the dealer keeps letting air out. Also, learn to use cruise control in town, if you don't already do this. That lets the hybrid computer maximize your mileage, instead of letting your right foot do it. Use SEARCH on this site, to find other tips to maximize your mpg's.
 
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