Old Topic but what the heck.... I always seem to get better MPG's from Pemex gas than California's gas.
There seems to be less difference between Arizona/Nevada/Utah as compared to Pemex.
Octane seems to be misunderstood to a certain degree. It is not a marketing ploy as Bob implies, it does actually make a difference, but he is
probably correct that most of us are just 'throwing' away our money using higher Octane.
Of course 'PREMIUM' fuels may more contain more detergents and stabilizers along with a Higher Octane number so it may be worth it.
HIGHER OCTANE FUEL IS LESS VOLATILE THAN LOWER OCTANE FUELS. In other words it is harder to ignite and possibly slower burning.
As fuel is compressed it also has a rise in temperature. If you continue to compress gasoline at some point it will ignite without any spark. In a
diesel engine that is what you want.
In a typical gasoline engine you want the spark to ignite the fuel at a set point in engine rotation (timing) or else you get the dreaded knock as the
fuel starts to burn on its own.
Since all cars have varying degrees of compression, some vehicles will compress the fuel more before igniting it with the spark. Up to a certain point
the further you compress the fuel before igniting it the more power you will get out of the fuel.
Now it is clear that lower compression engines will not knock on lower Octane fuel. Higher compression engines need higher Octane fuel to avoid
knocking.
Most common vehicles on the road today would be considered 'lower compression' vehicles so buying higher Octane fuel is not needed.
Now things are never as simple as that and in this case, as stated earlier, almost all vehicles made in the last 25 years have a Knock Sensor.
The cars onboard computer monitors the Knock Sensor and adjusts the engine, usually, by retarding the timing whenever it determines that knocking is
happening.
When you retard the timing you also decrease power output, so all your vehicles that 'run fine' on 85 or 87 octane might be doing so at the expense of
power output.
If you tow or live in mountainous terrain you might want to experiment with a higher Octane fuel. You might get better mileage and/or better
performance with higher Octane fuel.
For light loads, city driving for example, a lower octane may be fine. You need to experiment with different Octane fuels for your vehicle.
Now aside from Octane which is JUST the relative ease of a certain fuel to burn - lower octane=easier burning, higher octane=harder to burn, there is
also the matter of how much 'energy' is in the fuel and Ethanol certainly decreases the energy content, but so do other factors.
According to the EPA the energy content varies as much as 8% depending on the season and the producer.
It would therefore be possible to for Shell, Chevron, Mobil or some other name brand fuel to have 8% more energy in each gallon of gas which would
certainly result in better mileage such as DavidK reports.
Gasoline might be one of Americans largest expenses that we have no way of knowing what we are getting except by advertising and gut reactions. We
have no easy means to determine good/better/best between the all the gas stations we drive past every day.
Maybe fuel mileage should be expressed in miles per cents and not miles per gallon. So if I spend an extra 20 cents per gallon at Shell but go an
extra 2 miles is it worth it?
Here is a comparison ....
Arco is $3.00 per gallon and you get 15mpg with it.
Mobil is $3.20 per gallon and you get 16mpg with it.
Mobil is $3.20 per gallon and you get 17mpg with it.
Which is cheaper per mile...
Arco @15mpg =20 cents per mile
Mobil @16mpg = 20 cents per mile
Mobil @17mpg = 18.8 cents per mile
|
