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post #11 of 15 (permalink) Old 08-15-2009, 11:59 AM
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Default Re: Mileage drop off 2005 Prius

E10 is not the cause of a 10% drop in MPGs. E10 contains 97% of the energy of gasoline per gallon, so it causes about a 3% reduction in MPGs.

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post #12 of 15 (permalink) Old 08-17-2009, 02:00 PM
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Default Re: Mileage drop off 2005 Prius

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Originally Posted by richard schumacher
E10 is not the cause of a 10% drop in MPGs. E10 contains 97% of the energy of gasoline per gallon, so it causes about a 3% reduction in MPGs.
3% ? Nope more like 6-10%. The 3% calculates out probably because of the reduction in energy in a gallon if E10 gasoline, but it is only part of the story. All modern cars operate and control the fuel mixture by feedback from the oxygen sensor/s as you probably well know. The detection of left over oxygen in the exhaust means a lean incomplete burn so the ECM counters by enrichening the mixture. This happens in all computor controlled engines. E10 fuel (oxygenated fuel) leaves a bit of oxygen in the exhaust so it "tricks" the computor so to speak.
This is easily proven by the fact that an older carburated vehicle has much less mileage drop with the E10 gasoline.
Probably more like the 3% energy loss you mentioned.
I've talked to Toyota engineering about this, with the fact that they need to find a way to detect the presence of alcohol in the raw fuel and adjust engine parameters accordingly (ignition timing etc.) and so far no response. I believe this could recover much of the lost performance. Oh well I guess I will have to figure a way myself.
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post #13 of 15 (permalink) Old 08-17-2009, 05:17 PM
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Default Re: Mileage drop off 2005 Prius

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Originally Posted by Paul01
E10 fuel (oxygenated fuel) leaves a bit of oxygen in the exhaust so it "tricks" the computor so to speak.
That's an interesting claim. Do you have a source for it?

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post #14 of 15 (permalink) Old 08-17-2009, 10:01 PM
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Default Re: Mileage drop off 2005 Prius

I found it on the internet (of course) and I'll see if I can find it again and post one of the links I used. Also did some backyard engineering myself with the several vehicles I own, one carburated and one ECM controlled. Experimented with regular fuel and also E10 because my state was using both types of fuel then, one for summer the other for winter. It is all year E10 now however.
I took oxygen sensor readings with both fuel types and noticed a leaner voltage reading with the E10 therefore causing it to enrichen the mixture a bit more just like it is supposed to do. I knew how 02 sensors work and could not find any other reason for it to read differently except the fuel.
So-- after some internet reading and my own testing I kinda came up with some of my own conclusions I guess.
Still have my 2001 Prius and have kept records since day one. Used to get 50-53mpg in the summer, 45-46mpg in winter same roads same routes. Since E10 45-47mpg in summer and 42-44mpg in winter. Has not changed for the last couple years. Anyhow thats my story and I guess my opinion only at this point.
Auto makers may not care about incremental engineering changes at this point hence no responce from Toyota. Our cars are probably interem units while they work toward all electric ones in the future I suspect.
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post #15 of 15 (permalink) Old 04-03-2010, 01:08 PM
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Default Mileage drop off 2005 Prius

It might be a longshot, however people tend to leave their vehicles idling alot more, and tend to keep them on longer during the winter due to the cold. Is it possible that due to a colder winter, you start it and let it run for a bit when you get in? Doing so twice a day, daily could result in using more gas mileage. Or that you stay in it when going places and leave it running? Although this might not be the whole issue, it could be part of it.
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