re: "...Thinking further about this although more expensive would using premium grade higher octane gas give you greater miles per gallon ?..."
I always use premium (~93 around here), despite all the admonition that it's a waste from Conumers Reports and others of that ilk.
Here's why. Our cars are built (1) with knock sensors, and (2) for an optimum octane of around 91.
Now, first, we don't have 91 around here -- the choices are either 93 or 89 (or 87 for regular, which is a non-issue). Now, if I put in mere 89, the knock-sensor system will retard my ignition slightly when I'm driving "hard" (which is most of the time), and this retardation will lower my mileage (as well as my "fun factor").
The difference in price between 93 and 89 here is about $0.10 on a ~$3/gallon price, which is about a 3% difference (10/300). Yet I can expect a ~2 mpg benefit from premium, which is (very roughly) about 2/24mpg or ~8% gain.
Thus, simple cost-benefit analysis dictates that I'm better off spending ~3% more on the per gallon price of gas and reduce my volume consumption by 8%. That's a 2-3 times benefit over cost.
Use premium and you're ahead.
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