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As you know gasoline expands and contracts volumetrically with the temperature. The state "seals" of approval only account by testing the volume at the time (and temperature) that they do this. You get a more dense mix of molecules (higher concentrations per volume unit) at colder temperatures than you do at warmer temperatures.

I was wondering if you get more bang for you buck if you are always filling up earlier in the day instead of when it is warmer? If so, anybody know by how much?

Also, are the electronics in the car adjusting the mixture for the denser mix of gas at lower temperatures -vs- higher temperatures?

mdpc
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While the "earth mean temperature" will differ from one location to another the individual readings are quite stable year round. Gasoline storage tanks are typically underground. The soil acts as insulation or a buffer to temperature swings. What this means is that if the pumps were calibrated on an sunny summer day at 85 degrees the fuel temperature would be very close the ground temperature at 15 feet below grade. On a cool fall day say 40 degrees the fuel temperature will still be close to ground temperature. Modern engine control systems adjust the fuel mixture to maintain optimal fuel/air ratios in real time, meaning as the engine is running.

mikes
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  • I guess what you are saying is that it should be true that if you fill up when it is colder, you'll get more bang for your buck as the control systems adjust for the reaction concentrations based on temperature. – mdpc Jun 30 '15 at 18:40