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Are MPG ratings much less accurate then they used to be?



 
 
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  #1  
Old July 18th 05, 01:15 PM
General Schvantzkoph
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Default Are MPG ratings much less accurate then they used to be?

When I bought my old Concorde in 94 the MPG ratings were pretty much spot
on, the car got 22 in daily driving and 29 on long highway trips which is
what the window sticker claimed. The MPG ratings for the new 300C is 17
city/25 highway which isn't even close to the real values, I'm getting
15-16 in daily driving, just did a 220 mile round trip yesterday and it
peaked at 20 MPG. The article on hybrids (quoted in another thread) also
mentions that the real mileage is nowhere near the sticker values. So my
questions are these, has the method for determining the MPG ratings for
cars changed in the last 10 years? Have manufacturer's gotten better at
gaming the system? How do they determine the MPG ratings? It's hard to see
how Chrysler managed to come up with a 25 MPG highway rating on the 300C
unless they did the test on a road that was down hill all the way.

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  #2  
Old July 18th 05, 03:02 PM
Art
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AC is off during tests. That is why hybrids results are ridiculous. As for
the Hemi, perhaps it was optimized to turn off extra cylinders during the
test and your driving habits do not mirror those test circumstances.


"General Schvantzkoph" > wrote in message
news
> When I bought my old Concorde in 94 the MPG ratings were pretty much spot
> on, the car got 22 in daily driving and 29 on long highway trips which is
> what the window sticker claimed. The MPG ratings for the new 300C is 17
> city/25 highway which isn't even close to the real values, I'm getting
> 15-16 in daily driving, just did a 220 mile round trip yesterday and it
> peaked at 20 MPG. The article on hybrids (quoted in another thread) also
> mentions that the real mileage is nowhere near the sticker values. So my
> questions are these, has the method for determining the MPG ratings for
> cars changed in the last 10 years? Have manufacturer's gotten better at
> gaming the system? How do they determine the MPG ratings? It's hard to see
> how Chrysler managed to come up with a 25 MPG highway rating on the 300C
> unless they did the test on a road that was down hill all the way.
>



  #3  
Old July 18th 05, 04:18 PM
David
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Default


"General Schvantzkoph" > wrote in message
news
> When I bought my old Concorde in 94 the MPG ratings were pretty much spot
> on, the car got 22 in daily driving and 29 on long highway trips which is
> what the window sticker claimed. The MPG ratings for the new 300C is 17
> city/25 highway which isn't even close to the real values, I'm getting
> 15-16 in daily driving, just did a 220 mile round trip yesterday and it
> peaked at 20 MPG. The article on hybrids (quoted in another thread) also
> mentions that the real mileage is nowhere near the sticker values. So my
> questions are these, has the method for determining the MPG ratings for
> cars changed in the last 10 years? Have manufacturer's gotten better at
> gaming the system? How do they determine the MPG ratings? It's hard to see
> how Chrysler managed to come up with a 25 MPG highway rating on the 300C
> unless they did the test on a road that was down hill all the way.


The government determines the fuel consumption ratings not the Manufacturer.
The tests are conducted on a flat surface without using air conditioning,
and using average temperatures 70 - 80 degrees. And does not factor in,
stop and go driving ,or different road grades.


  #4  
Old July 18th 05, 04:41 PM
General Schvantzkoph
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Default

On Mon, 18 Jul 2005 14:02:45 +0000, Art wrote:

> AC is off during tests. That is why hybrids results are ridiculous. As for
> the Hemi, perhaps it was optimized to turn off extra cylinders during the
> test and your driving habits do not mirror those test circumstances.


Hard to believe that AC makes a 25% difference in a 4000lb car. The flat
surface for the government tests could be the reason for the huge
difference. 300Cs are very heavy and New England (where I live) is very
hilly even on highways. Lugging a 300C up a hill probably puts enough
strain on the system that all 8 cylinders are engaged which means that you
are going to use much more energy going up a hill then you get back going
down the other side because the engine is operating in it's less efficient
mode on the upside of the hill. I wonder how hybrids behave on hills. On
the one hand a true hybrid like the Toyotas will have to engage it's
gas engine more on the other hand they recover more energy on the down
side of hills because of the regenerative breaking.
  #5  
Old July 18th 05, 05:06 PM
wraithyjeep
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Actually MPG is determined by unused energy that is left in the emissions it
is a chemical analysis with factors of weight and other physics that overall
determines the MPG all this is done on a dyno. in a very controlled lab.
I used to know the formula (sorry be awhile since I worked in the lab)
the only way to truly achieve the listed MPG is with a lot of down hill
driving.


"General Schvantzkoph" > wrote in message
news
> When I bought my old Concorde in 94 the MPG ratings were pretty much spot
> on, the car got 22 in daily driving and 29 on long highway trips which is
> what the window sticker claimed. The MPG ratings for the new 300C is 17
> city/25 highway which isn't even close to the real values, I'm getting
> 15-16 in daily driving, just did a 220 mile round trip yesterday and it
> peaked at 20 MPG. The article on hybrids (quoted in another thread) also
> mentions that the real mileage is nowhere near the sticker values. So my
> questions are these, has the method for determining the MPG ratings for
> cars changed in the last 10 years? Have manufacturer's gotten better at
> gaming the system? How do they determine the MPG ratings? It's hard to see
> how Chrysler managed to come up with a 25 MPG highway rating on the 300C
> unless they did the test on a road that was down hill all the way.
>



  #6  
Old July 18th 05, 05:17 PM
Art
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Default

In the hybrid, as soon as AC goes on, gas engine goes on. That is why EPA
test results are a joke.


"General Schvantzkoph" > wrote in message
news
> On Mon, 18 Jul 2005 14:02:45 +0000, Art wrote:
>
>> AC is off during tests. That is why hybrids results are ridiculous. As
>> for
>> the Hemi, perhaps it was optimized to turn off extra cylinders during the
>> test and your driving habits do not mirror those test circumstances.

>
> Hard to believe that AC makes a 25% difference in a 4000lb car. The flat
> surface for the government tests could be the reason for the huge
> difference. 300Cs are very heavy and New England (where I live) is very
> hilly even on highways. Lugging a 300C up a hill probably puts enough
> strain on the system that all 8 cylinders are engaged which means that you
> are going to use much more energy going up a hill then you get back going
> down the other side because the engine is operating in it's less efficient
> mode on the upside of the hill. I wonder how hybrids behave on hills. On
> the one hand a true hybrid like the Toyotas will have to engage it's
> gas engine more on the other hand they recover more energy on the down
> side of hills because of the regenerative breaking.



  #7  
Old July 18th 05, 07:02 PM
damnnickname
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Default

They never were accuate. Those tests are done by starting the vehicle up
and driving with out a load on a lift and run untill the tank is empty,
There are no cold starts, (just one start up) no a/c or stop and go
traffic.
Glenn Beasley
Chrysler Tech

  #8  
Old July 18th 05, 08:04 PM
Percival P. Cassidy
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I don't recall what the EPA MPG ratings were for our '02 300M, but
driving back from Chicago to W. Michigan yesterday w. A/C on (outside
temp. in the 90s) the EVIC showed an average of a little over 27mpg.

BTW, does the grade (or brand) of gasoline affect mpg? I sometimes use
89, but mostly 87.

Perce


On 07/18/05 02:02 pm damnnickname tossed the following ingredients into
the ever-growing pot of cybersoup:

> They never were accuate. Those tests are done by starting the vehicle up
> and driving with out a load on a lift and run untill the tank is empty,
> There are no cold starts, (just one start up) no a/c or stop and go
> traffic.

  #9  
Old July 19th 05, 03:25 PM
Richard
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Default


"Percival P. Cassidy" > wrote in message
...
>
> BTW, does the grade (or brand) of gasoline affect mpg? I sometimes use 89,
> but mostly 87.
>
> Perce
>

No, except if the motor is into serious knocking. Too much octane is a waste
of money and resources.

Richard.


  #10  
Old July 19th 05, 03:35 PM
Daniel J. Stern
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Posts: n/a
Default



On Tue, 19 Jul 2005, "Richard" > wrote:

> > BTW, does the grade (or brand) of gasoline affect mpg? I sometimes use 89,
> > but mostly 87.


> No, except if the motor is into serious knocking. Too much octane is a
> waste of money and resources.


Outdated info, no longer correct. All modern engines use knock
sensors. Depending upon how the knock sensor and ignition timing control
is implemented and calibrated, using fuel of higher octane *can* improve
mileage by permitting more spark advance. Whether the increase in mileage
balances the increased cost of higher-octane fuel is situational.
 




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