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Evalutate the scientific correctness of this statement

sao123

sao123

Lifer
What time you get to the pump

Wednesday morning is the best time to buy gasoline according to GasPriceWatch.com. That's because prices usually move up for the weekend, after which they settle, hitting the low point by Wednesday.

And it makes sense to buy your gas in the morning when it's the coolest time of day. This is when gasoline is most dense. Gas pumps charge by the volume of gasoline, not the density, so in colder temperatures you'll get more for your dollar.


Sounds like crap fallacy to me, but im not 100% positive.
 
Ground temperature where the fuel is stored is relatively stable during the days temperature changes. News teams fails at science stuff
 
Originally posted by: sao123
What time you get to the pump

Wednesday morning is the best time to buy gasoline according to GasPriceWatch.com. That's because prices usually move up for the weekend, after which they settle, hitting the low point by Wednesday.

And it makes sense to buy your gas in the morning when it's the coolest time of day. This is when gasoline is most dense. Gas pumps charge by the volume of gasoline, not the density, so in colder temperatures you'll get more for your dollar.


Sounds like crap fallacy to me, but im not 100% positive.
Click to expand...


Hello all.

I have actually heard this, just recently too.
Would have to be pretty cool, but it does make a little sense, this is also why they say to not fill the tank completely full by constantly clicking the pump after it's stop, as gas will expand as it heats up. Just food for thought. May not be much, but when the prices are this high...
 
Originally posted by: OUCaptain
Ground temperature where the fuel is stored is relatively stable during the days temperature changes. News teams fails at science stuff
Click to expand...

QFT

I suppose if you live in a REALLY hot climate it might make a slight difference but is probably adjusted in these climates like silverpig said
 
Originally posted by: OUCaptain
Ground temperature where the fuel is stored is relatively stable during the days temperature changes. News teams fails at science stuff
Click to expand...

/nod This seems to me like another case where technically it's true in theory, but more or less negligible in practice. Now if one were to compare the actual energy density between the dead of winter and noon day summer in Chicagoland (or some other geographical region that actually experiences four seasons), I would expect there to be a difference.
 
The amount of volume change from the daily temperature swing in an underground tank is smaller than the smallest unit that the pump measures. On a day to day basis, there's no measurable difference. If you bought all your gasoline in the coldest part of winter you might save something like 0.8% compared to buying it on the hottest day of the summer. That's a whole $0.80 saved on $100 worth of gasoline.

From some numbers I ran a while ago:

The tanks are far enough underground that there's no significant change in temperature.

Ever gone into a root cellar in the middle of summer when it's ~100 out? It'll be ~60 degrees in the root cellar, and a root cellar isn't even completely buried. Put something 10-15 feet underground like a gas station's tanks are and you're talking about maybe, maybe a 15 degree swing in temperature from the coldest time in winter to the hottest time in summer. Daily fluctuation would be less than 1 degree.

For comparison, using measurements from a root cellar in Alberta, outside temperatures were less than -40 Fahrenheit and inside the root cellar the temperature was around 35 degrees (i.e. above freezing) but in the summer when temperatures were in the 90's the root cellar's temperature was around 50 degrees.

A 30 degree increase in temperature (from 60 degrees to 90 degrees) will cause an increase in volume of gasoline of 4 cubic inches. (From 231 cubic inches to 235 cubic inches.) Half of that increase, which represents the temperature change at tank depth equivalent to an above-ground swing of a staggering 130 degrees (remember that in the above example the below-ground temp changed from 35 degrees to 50 degrees when the above-ground temp changed from -40 to +90), would mean a change in volume from 231 cubic inches to 233 cubic inches. That's a change of 0.8% (0.008gallons) in volume from the coldest day of winter to the hottest day of summer. Change during the average day will be at most a single degree of fluctuation. Not enough to make any measurable difference.

ZV
 
Another fine example of why beat reporters should never be allowed to report on anything scientific, medical or technical. They NEVER get it right. And they usually cause some sort of panic. Not in this case...
 
Liquids tend to have very low expansion coefficients, and given the relatively constant temps of the underground tanks, I doubt there's much effect.
 
thats the same exact wording from a chain letter email that we've all probably received. they were talking about it the local radio show today as well.

plus, this is a repost.
 
Originally posted by: Whoozyerdaddy
Another fine example of why beat reporters should never be allowed to report on anything scientific, medical or technical. They NEVER get it right. And they usually cause some sort of panic. Not in this case...
Click to expand...

They probably got this out of a chain e-mail. It wouldn't be the first time such a thing went on to become "news."
 
Originally posted by: sao123
And it makes sense to buy your gas in the morning when it's the coolest time of day.
Click to expand...


incorrect, morning is not the coolest time of the day.

This is when gasoline is most dense. Gas pumps charge by the volume of gasoline, not the density,
Click to expand...

correct.

so in colder temperatures you'll get more for your dollar.
Click to expand...

a dollar is worth one dollar no matter if the air is 0 degrees or 100 degrees.
 
Originally posted by: Whoozyerdaddy
Another fine example of why beat reporters should never be allowed to report on anything scientific, medical or technical. They NEVER get it right. And they usually cause some sort of panic. Not in this case...
Click to expand...

add to that business and economics please, though that probably falls into the technical category.
 
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