[Bridey]

I think buying gas real cheap is a false economy. Last year I had lots of problems with my car cutting out or 'coughing' down the street. The garage told me it was caused by dirty (cheap) fuel.

[Kohn]

That's scary. That can even be criminal. Can gas companies dilute fuel the way you seem to imply? You see, the fuel that we buy come almost from the same refineries, unless I'm mistaken.

[FiveSpeed]

No, it all comes from the same refineries, but different brands mix in different additives. For instance, Brand A might mix in a 25:100 ratio of detergents (necessary to keep fuel systems clean), while Brand B might only mix in a 5:100 ratio. And sometimes, older, less used tanks contain water. I recommend always buying from a busy, well trafficked station. And buy name brand gas, not some brand no one's ever heard of.

[Max]

It is possible to get gas tainted by moisture. Keeping your tank topped off can help prevent moisture forming in your tank as well.

[Bridey]

I never thought of the moisture aspect. It is definitely good advice to go to a well used gas station. I don't think the problems I had were caused by malicious tampering, more likely 'bottom of the barrel' fuel.

[Tabby]

My dad always tells me to fill up when it hits a quarter tank and not to let it get empty, especially in winter. I wonder if that's because of the moisture build-up?

[Mario]

There are additives you can buy to add to your gas tank which can help eliminate any. moisture. They are more commonly used in the winter as a preventative measure.