Have you? I fill up at the 'sketchy' gas stations in town as they are the cheapest. Everyone tells me that the gas at these stations are "watered down" or "past its expiry date", yet I find virtually no difference in MPG when compared to fills at brand name gas stations.
I don't know if their is any difference in mileage or not.
I typically run just Chevron gas. I had several occurances, at different gas stations, where I got gas that was either very old, or something and it plugged up the fuel system from back to front. I finally switched to using just Chevron, largely and I haven't had any substantial fuel delivery issues in the years since then. Since I haven't had any of the previous issues, I've decided to just pay Chevron for the privilege of having either fresher gas, or better gas, or cleaner gas, or whatever it is that makes it so I don't have to work on the fuel delivery system.
I've tried 5 different brands with no noticable FE change. I don't think you'll see a noticable difference in gas but I guess we could start a discussion about additives. Puts on fire suit. I think you do get what you pay for.
I don't know about bad gas FE, but bad gas does exist. My buddy filled his Nissan truck in Kokadjo, Maine, and it almost died. He had to drive it home 300 miles sputtering and coughing all the way. He took it to the dealer who had to blow out the entire fuel system to get it to run smoothly again.
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