Originally Posted By: HangFire
Any individual gas station can have bad gas while others do not, due to condensation or water infiltration. Infiltration can happen from something as simple as a poorly secured or sealed tank fill cap and a good soaking rain. As already commented, the very busy stations are better, because there is less time for the condensation to build up, but the tank levels still cycle and still need make-up air and that make-up air has water humidity in it the outside air has.
But what does water have to do with poor fuel economy?
Ethanol gas like E10 doesn't suspend water in gas like methanol (dry gas) does. Quite the opposite it phase separates and pulls itself and the water from the gas in a separate layer. On top of that it is hydrophyllic and sucks the humidity out of the air. If, during a fillup, you draw from that phase separation layer, you get something like E15 or E20 or worse, with extra water.
Modern engines will self-adjust and deal with the high E and low gas content, but of course high E gas has lower energy content per unit. Thus lower fuel economy.
So one possible explanatation for your low fuel economy is that you're running something like E15 or E20 with extra water. As long as you keep driving it'll keep the water mixed up enough to burn OK.
My pickup gets only weekly use and sometimes skips a week. When using E10 it would rough start, stumble and cough and even die for several minutes after starting. If I took it for a long drive it would run fine for the rest of the day, then a week later with no fill-up do the same thing on startup. It did this for 2 years.
Once I switched to e-free gas the problem went away, with no other changes performed to the engine or tune-up. The problem was condensation and phase separation using E10 gas.
This is a good explanation. My current tank of wawa gas seems to be doing much better than the previous fill up. Possibly it did contain more ethanol. My maxima' fuel diet for most of its life has been sunoco. Sometimes wawa, once in a while exxon. So 70% sunoco, 20% wawa, 10% of whatever. And i am never touching shell,that stuff just dissapears from my gas tank. To a couple of other comments thank you for your input.
Oh and i was a bit [censored] when i made this thread so i kind off had to vent a little.