SS2006 wrote:how does MIdgrade do btw..?
It depends on what you mean by midgrade. In the United States, it is usually a mixture of 90% 87 octane unleaded regular and 10% ethanol and is called E-10. The ethanol raises its octane to 89. (Long ago, before ethanol, a few oil companies, such as Sunoco, had several grades that were mixtures of regular and premium. The mixing was done by the gas pump according to the octane you selected.)
Because ethanol has 30% less chemical energy than gasoline, E-10 has 3% less energy than straight gas (E-0). Therefore, you should expect mpg to be 3% lower with E-10. This is almost undetectable on the road. Lifetime average consumption for my G37 is 23.4 mpg. Three percent of that is only 0.7 mpg. My gas mileage varies that much from tank to tank even with the same fuel.
It is very difficult to measure fuel consumption on the road. Consumption is affected to a significant degree by factors such as barometric pressure, air temperature, humidity and fuel chemistry which varies from tank to tank. But those are small compared to changes in driving. That's why the EPA gives separate city and highway mpg estimates. It matters even more whether you poke along like grandma or drive it like you stole it. What you really need is an engine test cell with many thousands of dollars of instrumentation where you can control the driving and compensate for the other factors during data analysis.
Whenever I buy gas for our Subaru, which does run on 87 octane, I compare the prices of E-10 and E-0. Right now, E-0 is about $2.60 per gallon and E-10 is $0.15 cheaper which is 6% less. Therefore, I have been buying E-10 on the premise that I save more on price than I lose on increased consumption. If E-0 were to go above $5.00 per gallon and the difference remained at $0.15, the reverse would be true and I would save money by paying extra for E-0.
When shopping for what became my G37S, I gave considerable thought to fuel consumption. My conclusion was that depreciation, maintenance, insurance and licensing were bigger concerns than the difference between 20 mpg and 30 mpg and whether my car burned regular or premium.
