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

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.

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.

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.

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.

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

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

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

Perce

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

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

Richard.

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.

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

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

Perce

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

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.

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?

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:

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

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.

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