More Sun, Less Gas

By Deane Barker on July 5, 2007

Motorists steamed over ‘hot fuel’ losses sue oil titans, retailers: When it gets hotter, gas expands. Ergo, you get less gas at the pump for the same amount of money.

Predictably, someone is suing.

The price of gas has been based since the 1920s on a formula that measures a gallon of gas when it is 60 degrees, according to court papers filed by motorists.

According to industry and government standards, a gallon of gas at 60 degrees measures 231 cubic inches. Consumers buy 231 cubic inches of gas per gallon, regardless of its temperature, so when gas expands in the heat, the amount of energy put out per gallon declines.

I wonder how much this is offset by how the temperature fluctuations affect the performance of your car. At colder temperatures, air is denser, so engines perform better. This means one of two things:

  1. You have to give the engine less throttle to get the same acceleration, thus saving you gas.

  2. You just spend more gas because your engine injects more fuel to compensate for the denser air.

So, the “hot fuel” problem at the pump is either all or partially canceled out, or it gets worse. I know, I know — I’m helpful.



  1. One more factor: warmer air=less wind resistance… I’ve gotten my best MPG in hot weather.

  2. The temperature of the gas is not equal to the temperature of the air. Gas is stored in underground tanks, so it will remain cooler on hot days (Same principle as geothermal heating/cooling). Anybody actually measure the gas temperature before we get all wound up over something that may not be a problem?

  3. Given that it was apparently a big enough issue that they’ve installed temperature correction equipment in places where it’s routinely colder than 60 degrees, I think there might be a good basis here.

  4. Two things come to mind here regarding fuel and the effect of temp.

    One, this is why jets do not deal with gallons, instead the pilot orders his fuel by the pound. The energy in a pound of jet fuel is constant, or nearly so with regard to temp variations. The fueler then takes the pounds order, consultes a handy booklet that tells him how many gals to put in at the current ambient temp to achieve the energy the pilot needs. The fuel is still sold bu the gal however and costs about 50% more on the airfield than off. This ‘flowage fee’ helps the airport function.

    With regard to gasoline and Cars, the temp issue is minor as fuel is almost universally stored underground and the temp variation from day to day is minor. It would be interesting to have a display on the pump that said how much above or below ISO std. (59F or 20C) the fuel was that day. Geeks would make out with cooler fuel. MH

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