Thread: Gas Buying Tips
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Old 09-27-2007, 04:31 AM   #6
indydave
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Join Date: Jun 2007
Location: Indianapolis
Posts: 8
The temperature thing is probably only true for a short period of time after the gas is delivered. Once the gas in in the tanks underground, I doubt that there's much temperature variation over the course of a day.

Here's another interesting Gasoline fact: Ethanol has only about 70% the energy density of gasoline. Vehicles that run E85 typically get 25-30% less MPG than on Gasoline.

This effect is also present when you buy gas that's 10% Ethanol. Since that 10% of the fuel has only 70% of the energy of the rest the rest of the gasoline, the overall energy density of the fuel (compared to gasoline) is (.90*100%)+(.10*70%)=97%. This means your gas mileage WILL be reduced by 3% if you use the 10% Ethanol blend. If your Boxster gets 25.00 MPG on regular Gasoline, it will get 24.25 MPG on the 90/10 blend.

The 90/10 blends are a bad deal unless the price is less than 97% of the price of 100% Gasoline: If Gas is $3.00 a gallon, you'd have to buy the 90/10 blend for $2.91 or less to break even.

There are some other things to worry about with ethanol, too, but the economics alone usually make it a poor bargain.
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