Hot Weather, Less Fuel

Last week whilst at the pump in the hot, hot, hot Summer afternoon of 2:30pm, I realised that I was paying the same amount to fill up, however the same amount of fuel was taking me lesser distance, i.e. I had to refuel earlier than expected (I have a habit of always zeroing the (A) mileage when refueling, hence I calculated that I should be doing an average of 330KM before I need to refuel, at present I had done only 290 and it was time to head back to the pump).

At first, I viewed it as an annoyance rather than a monetary problem. However, the wheels started turning upstairs, and I wondered why?

Enter the Google.

A short search later, I came across a post entitled “Pain in the Gas” (here) which confirmed my intial suspicion; when you fuel up in the heat, you are getting less umph per litre. The fuel is more volatile, and therefore “lighter” than it should be when the weather is more humane, I mean colder.

The jist of that article:

No matter when you buy a gallon of gas, you get 231 cubic inches. But the number of British thermal units or Btus varies depending on the temperature of the fuel. A Btu is the amount of heat required to increase the temperature of one pound of water one degree Fahrenheit or the amount of energy in the fuel.

The gas will expand or contract one percent for every 15-degrees above or below 60 degrees. In other words, the fuel contracts in the cold. So when you buy a gallon, you get more energy for your money. In the heat, just the opposite is true: even though you’re still buying a gallon of gas, you get less energy for your money than you do in cold weather.

A one-percent variation doesn’t mean much when gas is selling for $1 or even $2 a gallon. But it makes a difference when you’re paying $4 or more a gallon.

Don’t get me wrong, you are getting the same amount of fuel, but since its already “hot” given the heat, it burns faster, making it more volatile, and taking you for less distance. Think of it like Vimto; when you add too much water, you still get the lovely Vimto taste, however it is diluted.

So to those with Big Gas Guzzlers, fuel up when the sun goes down, you will get more mileage per litre.

We live in Kuwait, where a litre of fuel is literally, cheaper than a litre of water. (almost everyone uses the 65fils per litre fuel, where as 600ml of water cost 100fils).

And that concludes our science portion of the day.

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