Originally Posted by 00 Trans Ram
You can do research yourself, but what you will find is that . . . Sam's is just fine. In fact, probably better than most.
First off, all gas is the same (or damn close). After all, think about it - does Sam's, or Costco, or Circle K, or 7-11, etc. have their own refineries? Nope. They buy their gas from the same few petrochemical companies - Shell, Conoco, BP, Valero, etc.
Also, those companies buy their "base gas" (gasoline before additives) from each other! A Shell refinery may refine crude from a BP oil rig, then sell it back to BP as gasoline.
And, a word about "additives". They really don't help all that much. By far the most important additive is detergent that helps prevent sludge from building up on intake valves. However, because our cars are direct injected (gas injected AFTER the valves, directly into the combustion chamber), all that detergent just gets burnt up without helping at all. They can help keep injectors clean. But, frankly, injectors can last a hundred thousand miles or more before degrading enough to need cleaning. And then, just add some over-the-counter injector cleaner for $5.
By far the most important factors in gasoline choice are:
1) age of the gas (how long does it sit in the underground tanks at the fill-up station)
2) age of the equipment at the fill-up station
Gasoline is hygroscopic. It attracts water (from the air, mostly). The longer it sits, the more water it attracts. Now, I did some calculations way-back-when (when I was racing karts and cars), and you really have to let it sit a while (months in a plastic gas jug) before it attracts enough water to degrade performance. But, you don't want gasoline just sitting in an underground tank.
So, how do you know how long the gas has been sitting there? You don't. But, the busier the gas station, the less time it is sitting in the tanks. The Sams near me fills up it's tanks once every 1.5 days. That means that the gas going into my tank has been sitting in the underground tank, on average, around 18 hours. That's not enough time for ANYTHING to happen to it (assuming good equipment).
Coincidentally, the stations that need the most-often refillings, also tend to have the lowest prices. Because most people are going to places with low prices.
The second point (age of equipment) is also easy to deduce. If the station looks crappy, then their underground tanks and pumps are also probably crappy. They may not be sealed. They may let water in. They may let gas vapors escape. But, if it all looks good above ground, it's probably good underground, too. My Sams replaced their pumps and tanks about 5 years ago, so they still have that "new pump smell" (hahaha).
TLDR - Find the best-looking station with the most traffic (and usually cheapest prices), and you've found the best gas.
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