Our local Mobil station sells octane gas for cents a...

Dear Car Talk

Dear Car Talk | Jun 01, 1994

Dear Tom and Ray:

Our local Mobil station sells 87 octane gas for 99 cents a gallon. They sell 89 octane for $1.19 a gallon, and they sell 93 for $1.25 a gallon. My car uses 89 octane. If I use half a tankful of 87 octane, and half a tankful of 93 octane, won't I get 90 octane gas? And won't it cost $1.12 a gallon, which is seven cents less than the cost of their 89 octane? Does octane work this way?

RAY: Geez, Dave! You have uncovered one of the most insidious, sinister marketing plots ever foisted upon us by the military-industrial-fruit- growing complex. Good work! We've already called Oliver Stone, and he's working on a feature length movie about this for next summer.

TOM: Octane DOES work that way, Dave. In this range--between about 85 to 95--octane blends linearly. That means if you mix half a gallon of 87 with half a gallon of 93, you'll get the average of the two: 90 octane.

RAY: And in this case, as you have so wisely deduced, you'll save a few cents a gallon, too.

TOM: In fact, if you go to a Sunoco station, that's how they get all those different grades of gasoline they sell. You think they have a tank of 86, a tank of 87, and tank of 88, 89, 90 etc.? No. They have one tank of the good stuff, and one tank of "balsamic vinegar." And when you dial your selection on the pump, the two get blended together right there on the spot to give you what you want.

RAY: And there's nothing wrong with that. But we agree with you, Dave, that the price ought to be linear, too, so you don't have to waste your time mixing gasolines. So here's what we propose. Go back to your gas station, and ask "Butchie" to add one gallon of 87, and then one gallon of 93--and ask him to keep alternating--until your tank is full. And when he complains, explain to him why you're doing it.

TOM: And if you really want to drive the point home, wait until the next torrential downpour before you do this! 1947

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