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

On 07/19/05 10:25 am Richard tossed the following ingredients into the
ever-growing pot of cybersoup:

>>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.

The Owner's Manual for our '02 300M says 87 is acceptable, but 89 is
preferable -- but doesn't say why.

Perce

"Daniel J. Stern" > wrote in message
n.umich.edu...
>
>
> 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 Outdated info, no longer correct.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.

Yes, but too much octane is a waste of money and resources. If a vender
recommends something higher than 87 but allows 87 as an alternative, then
your comments are on point. One benefits from the higher octane the most on
a hot day pulling a load, but your point is well taken.

Richard

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

> > 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.
>
> Yes, but too much octane is a waste of money and resources.

Depending on 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. Which
part of that is hard for you to understand, Richard? If using
higher-octane fuel nets sufficiently higher mileage to more than offset
the increased cost per unit volume of the higher-octane fuel, then it is
neither too much octane nor a waste of money.

"Percival P. Cassidy" > wrote in message
news
> On 07/19/05 10:25 am Richard tossed the following ingredients into the
> ever-growing pot of cybersoup:
>
> >>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.
>
> The Owner's Manual for our '02 300M says 87 is acceptable, but 89 is
> preferable -- but doesn't say why.
>
> Perce

If that's what the owners manual says then do not use a higher octane rated
fuel. It will cause more drivability problems and leave more deposits in the
combustion chamber possibly causing a pinging problem
It will not improve MPG . If anything it will cause a lower MPG over a
period of time.
Glenn Beasley
Chrysler Tech

"maxpower" > wrote in message
...
>
> "Percival P. Cassidy" > wrote in message
> news
>> On 07/19/05 10:25 am Richard tossed the following ingredients into the
>> ever-growing pot of cybersoup:
>>
>> >>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.
>>
>> The Owner's Manual for our '02 300M says 87 is acceptable, but 89 is
>> preferable -- but doesn't say why.
>>
>> Perce
>
> If that's what the owners manual says then do not use a higher octane
> rated
> fuel. It will cause more drivability problems and leave more deposits in
> the
> combustion chamber possibly causing a pinging problem
> It will not improve MPG . If anything it will cause a lower MPG over a
> period of time.
> Glenn Beasley
> Chrysler Tech

Don't you mean a lower octane? Since when does higher octane cause more
deposits?

"David" > wrote in message
news:GDdDe.156426$go.138281@fed1read05...
>
> "maxpower" > wrote in message
> ...
> >
> > "Percival P. Cassidy" > wrote in message
> > news
> >> On 07/19/05 10:25 am Richard tossed the following ingredients into the
> >> ever-growing pot of cybersoup:
> >>
> >> >>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.
> >>
> >> The Owner's Manual for our '02 300M says 87 is acceptable, but 89 is
> >> preferable -- but doesn't say why.
> >>
> >> Perce
> >
> > If that's what the owners manual says then do not use a higher octane
> > rated
> > fuel. It will cause more drivability problems and leave more deposits in
> > the
> > combustion chamber possibly causing a pinging problem
> > It will not improve MPG . If anything it will cause a lower MPG over a
> > period of time.
> > Glenn Beasley
> > Chrysler Tech
>
> Don't you mean a lower octane?
No

Since when does higher octane cause more
deposits?

Since certain vehicles were designed to use it depending on the
compression ratio. The octane rating of gasoline tells you how much the
fuel can be compressed before it spontaneously ignites. When gas ignites by
compression rather than because of the spark from the spark plug, it causes
knocking in the engine. If a vehicle that is designed to use a low octane
fuel 87-89 uses high octane fuel consistently 93+(slow burning fuel) it
leaves deposits on the pistons, valves and so on.
This will eventualy cause compression problems.
Im no chemist and im sure there are people on here that may be able to
explain it better, but i will say this, I have pulled down many heads from
vehicles that have excessive amounts of carbon deposits on the valves ( caus
ing lack of compression, check engine lite on) because the owners insist on
using the wrong octane rated fuel in their vehicles, And Chrysler does not
warranty fuel related problems either

On Tue, 19 Jul 2005 17:33:43 -0400, maxpower wrote:

>
> "David" > wrote in message
> news:GDdDe.156426$go.138281@fed1read05...
>>
>> "maxpower" > wrote in message
>> ...
>> >
>> > "Percival P. Cassidy" > wrote in message
>> > news >> >> On 07/19/05 10:25 am Richard tossed the following ingredients into the
>> >> ever-growing pot of cybersoup:
>> >>
>> >> >>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.
>> >>
>> >> The Owner's Manual for our '02 300M says 87 is acceptable, but 89 is
>> >> preferable -- but doesn't say why.
>> >>
>> >> Perce
>> >
>> > If that's what the owners manual says then do not use a higher octane
>> > rated
>> > fuel. It will cause more drivability problems and leave more deposits in
>> > the
>> > combustion chamber possibly causing a pinging problem
>> > It will not improve MPG . If anything it will cause a lower MPG over a
>> > period of time.
>> > Glenn Beasley
>> > Chrysler Tech
>>
>> Don't you mean a lower octane?
> No
>
> Since when does higher octane cause more
> deposits?
>
> Since certain vehicles were designed to use it depending on the
> compression ratio. The octane rating of gasoline tells you how much the
> fuel can be compressed before it spontaneously ignites. When gas ignites by
> compression rather than because of the spark from the spark plug, it causes
> knocking in the engine. If a vehicle that is designed to use a low octane
> fuel 87-89 uses high octane fuel consistently 93+(slow burning fuel) it
> leaves deposits on the pistons, valves and so on.
> This will eventualy cause compression problems.
> Im no chemist and im sure there are people on here that may be able to
> explain it better, but i will say this, I have pulled down many heads from
> vehicles that have excessive amounts of carbon deposits on the valves ( caus
> ing lack of compression, check engine lite on) because the owners insist on
> using the wrong octane rated fuel in their vehicles, And Chrysler does not
> warranty fuel related problems either

I just checked the owners manual for my 300C and it says that use of
premium fuel is not recommended. If an engine like the 5.7L Hemi doesn't
use premium fuel what does? Are there any modern engines that need premium
fuel or are the oil companies just counting on consumer ignorance to get
an extra dime a gallon?

On 07/19/05 07:27 pm General Schvantzkoph tossed the following
ingredients into the ever-growing pot of cybersoup:

> I just checked the owners manual for my 300C and it says that use of
> premium fuel is not recommended. If an engine like the 5.7L Hemi doesn't
> use premium fuel what does? Are there any modern engines that need premium
> fuel or are the oil companies just counting on consumer ignorance to get
> an extra dime a gallon?

What do you/they mean by "premium"? 93 Octane, 91, or only 89? ISTR that
DC recommended 93 Octane (or perhaps it was 91) for the '02 300M Special
*if one wanted the maximum power*, otherwise 89 Octane would do. As I
wrote earlier, for the regular '02 300M they said that 87 is OK but 89
is better -- or perhaps they used the phrase "for optimum performance."

AFAIK, all kinds of factors could affect the required Octane rating,
e.g., size and shape of the combustion chamber, as well as the
compression ratio.

Perce

On Tue, 19 Jul 2005 19:48:16 -0400, Percival P. Cassidy wrote:

> On 07/19/05 07:27 pm General Schvantzkoph tossed the following
> ingredients into the ever-growing pot of cybersoup:
>
>> I just checked the owners manual for my 300C and it says that use of
>> premium fuel is not recommended. If an engine like the 5.7L Hemi doesn't
>> use premium fuel what does? Are there any modern engines that need premium
>> fuel or are the oil companies just counting on consumer ignorance to get
>> an extra dime a gallon?
>
> What do you/they mean by "premium"? 93 Octane, 91, or only 89? ISTR that
> DC recommended 93 Octane (or perhaps it was 91) for the '02 300M Special
> *if one wanted the maximum power*, otherwise 89 Octane would do. As I
> wrote earlier, for the regular '02 300M they said that 87 is OK but 89
> is better -- or perhaps they used the phrase "for optimum performance."
>
> AFAIK, all kinds of factors could affect the required Octane rating,
> e.g., size and shape of the combustion chamber, as well as the
> compression ratio.
>
> Perce

Premium is defined as 91 or higher. The 300 owners manual says use 87 for
the 2.7L engine, 89 for the 3.5L and 5.7L. It also says that use of
premium fuel is not recommended. Don't know if that's because it's a waste
of money or because it damaging as maxpower suggested.

In article >, says...
> 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.
>

Interesting. On a recent 280 mile trip my 2000 3ooM achieved 27.8 mpg on
the interstates, full vacation load, wife, kids, dog, full trunk, etc.

I usually get a max of 26.5 mpg. Only changes were a fresh load of Mobil
1 10-w30 synthetic oil , try to keep it down to 65 mph, and 32 psi in
the tires (my old tire gauge was giving false readings, about 3 pounds
low)