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post #1 of 21 (permalink) Old 11-14-2005, 01:20 PM Thread Starter
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Default mileage in slow decline

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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post #2 of 21 (permalink) Old 11-14-2005, 01:59 PM
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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.

Hep
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2004 Tideland Pearl now belongs to my daughter.
2010 with all the whistles and bells is MINE!
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post #3 of 21 (permalink) Old 11-14-2005, 02:19 PM
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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?

2005 Prius - Tideland #6
Matrix Bumper Protector, EV Switch, NAV/Phone Speed Sensor Defeat Switch, Kenwood w00x Subwoofer, Aftermarket speakers and tweeters, DICE Ipod Interface, 2\" Trailer Hitch
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post #4 of 21 (permalink) Old 11-14-2005, 02:20 PM
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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

If you're coasting, you're going downhill...or else you're in a Prius with no arrows.

S/W Ohio, '05 Driftwood Pkg #6
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post #5 of 21 (permalink) Old 11-14-2005, 04:44 PM Thread Starter
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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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post #6 of 21 (permalink) Old 11-15-2005, 08:59 AM
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Techron-based fuel line/fuel injector cleaner?...

2004 Seaside Pearl #9/BC since 1/3/04, running Amsoil Series 2000 0W-30 synthetic oil
Goodyear TripleTred 195/65R15 tires since 5/19/05
60,000 miles as of 3/22/2007
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post #7 of 21 (permalink) Old 11-15-2005, 09:56 AM
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Quote:
Originally Posted by moocatdog
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?"

Hep
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2004 Tideland Pearl now belongs to my daughter.
2010 with all the whistles and bells is MINE!
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post #8 of 21 (permalink) Old 11-15-2005, 10:19 AM Thread Starter
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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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post #9 of 21 (permalink) Old 11-15-2005, 10:33 AM
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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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post #10 of 21 (permalink) Old 11-15-2005, 02:57 PM
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Quote:
Originally Posted by DanMan32
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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