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post #1 of 15 (permalink) Old 08-12-2009, 01:22 PM Thread Starter
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Default Mileage drop off 2005 Prius

Haven't been here for a while but have a concern about deteriorating fuel mileage in my 2005 Prius. I am located in Vermont, rather mountainous driving. This car has 83,000 miles. The average summer MPG of this car (originally purchased new June '05) is: 2005: 53, 2006: 55, 2007: 54, 2008: 52, 2009: 49--a loss of 6 MPG from peak mileage attainted. It has been a cooler, wetter summer than normal which I estimate to be a 1.5 MPG negative. Some other factors: I am driving the same way as always: pulse and gliding sometimes; come up slow on red lights, etc. On third set of tires: Goodyear Integrity with 8,000 miles wear (psi: 40 lbs. front/38 lbs. rear), always make sure oil not overfilled at 5,000 oil change/servicing.

I talked to my local Toyota service dept. They come up with possibilities of inverter coolant needing changing (normally done at 90,000) and spark plugs (also 90,000). Wondering if anyone has other ideas, or have also had deteriorating mileage in an older Prius.
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post #2 of 15 (permalink) Old 08-12-2009, 02:02 PM
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Default Re: Mileage drop off 2005 Prius

My guess is the colder, wetter summer has contributed to most of your MPG loss. I doubt that the inverter coolant or spark plugs are contributing.
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post #3 of 15 (permalink) Old 08-12-2009, 02:16 PM Thread Starter
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Default Re: Mileage drop off 2005 Prius

Firepa63 - Thanks for the feedback. I have driven at least two tankfuls this summer where the weather has been mostly dry and warmer, but have never done better than 50.5 MPG. In '06 and '07 I would normally get 54-55, even using some AC and with some rain. It's definitely more than weather related.
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post #4 of 15 (permalink) Old 08-12-2009, 05:50 PM
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Default Re: Mileage drop off 2005 Prius

Any change in gasoline, like 10% ethanol?
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post #5 of 15 (permalink) Old 08-13-2009, 03:32 PM
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Default Re: Mileage drop off 2005 Prius

I usually get 53-55 mpg in the winter and 46-47 in the summer (due to air conditioner use). However, this past month we have been hitting 110+ degrees F pretty consistently, and the mileage has really gone in the tank. I had one fillup at 39 mpg, and most others have been around 41-42. The weather can really affect your mileage, unless you just leave the heater or AC off and just bear with the uncomfortable weather.

Our best mpgs are in the spring and fall when the daytime temps are between 65 and 85, and I drive with the windows down and everything off.
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post #6 of 15 (permalink) Old 08-13-2009, 06:20 PM
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Default Re: Mileage drop off 2005 Prius

Four year old plugs and 80,000 miles on 10% enthanol. Not an expensive fix! I'de change them.



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post #7 of 15 (permalink) Old 08-13-2009, 09:04 PM Thread Starter
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Default Re: Mileage drop off 2005 Prius

The ethanol makes some sense. I noticed the 10% label on the tank at Sunoco yesterday. I'm wondering if the 10% has been a year round additive until this summer? And Phoenix, my seasonal mileage has been the direct opposite of yours in my northern region, except no longer this summer. I'll go for the new plugs and perhaps change the inverter fluid at 85,000.
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post #8 of 15 (permalink) Old 08-14-2009, 09:34 AM
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Default Re: Mileage drop off 2005 Prius

Enthanol is a political thing. Although the exhaust emmissions are slightly reduced, this benefit is cancelled because their are more of them because of reduced milage. They were once state required but I believe it became a federal mandate for all states slightly before the Iowa caucasus in the last election. (Your politicians "at work.")



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post #9 of 15 (permalink) Old 08-14-2009, 02:56 PM
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Default Re: Mileage drop off 2005 Prius

Oxygenated fuels are required in Arizona part of the year. This is not a new requirement to subsidize the ethanol industry, but has been a long-time requirement (at least in Arizona), for smog control.

My mileage has been creeping up a little this week, and our 2002 Prius is almost up to 44 mpg -- It's only been in low-100's! Can't wait until it gets in the mid-90s again, so I can roll my windows down.
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post #10 of 15 (permalink) Old 08-14-2009, 04:57 PM
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Default Re: Mileage drop off 2005 Prius

All points true. But the smog advantage is eliminated because you have to burn more of the 87 octane because of the drop in milage. Ditto on savings from the purchasing middle east oil.
Ten per-cent ethanol destroys lifespan of fuels in tanks for lawn mowers, boats and the government has forbid it's use in aircraft that have been certified for use with auto fuel. God onlyy knows what it does on "O" rings in injection systems. We already know it destroys carbuerators.
It's a political thingy. Just more government control of citizens.



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