Comments on: Morning Fill ‘Er Up

By: 3 thingsabout money

3 thingsabout money — Wed, 11 Apr 2007 10:23:49 +0000

The metapoint of this is less about the 3 cents and more about planning. I save a lot of money on gas when I *plan* my purchases, know when they’re coming, reduce driving, and yeah, fill up in the morning. The worst is when I am randomly low on gas. Nice post, (and I loved my physics lesson from Savvy Steward up yonder.)

By: Debt Hater

Debt Hater — Tue, 10 Apr 2007 03:00:30 +0000

I think the only way to save gas is not to drive so often. The other day I read an article about saving money on gas or improving mileage by keeping the windows rolled up if you’re going 55 mph or faster and blah blah blah. But when the weather is nice, what’s the fun in that! I’ll sacrifice a few pennies to feel the wind. If I’m that worried about gas, I’ll walk or stay home.

By: mapgirl

mapgirl — Tue, 10 Apr 2007 01:51:15 +0000

Great comment Savvy Steward! The tanks are underground and unless the ground temperature changes a lot, I guess it’s safe to buy gas at almost any time of day. I wonder if there is better insulation with double hulled tanks?

Hm… It does make me think hard though. My pop used to get most of his deliveries at night. Trucks would come there after making deliveries at other stations, and then dump whatever they had left into his tanks. Rarely did we take a delivery during daylight hours. (We were a 12 pump station in PA with some serious capacity. IIRC, about 20K gals total.)

By: Zachary

Zachary — Tue, 10 Apr 2007 01:50:46 +0000

Gotta love physics and personal finance.

By: Around the PF Blogosphere: April 9, 2007 | The Sun’s Financial Diary | A Personal Finance Blog on Saving and Investing

Tue, 10 Apr 2007 01:45:52 +0000

[...] Mapgirl’s Fiscal Challenge argues you should fill up your tank in the morning, because “the temperature is coldest and you get more gas in your tank.” That’s a surprise! [...]

By: Savvy Steward

Savvy Steward — Tue, 10 Apr 2007 00:05:40 +0000

I’m a mechanical engineer by trade so I’ll have to comment on this:

Assuming that the volumetric CTE (coefficient of thermal expansion) of gasoline is 950 x 10 -6 per Celsius

From 50F to 70F is a 20F rise or 11.1C rise in temperature.

0.000950 * 11.1C = 0.01 (a 1 percent increase in volume based on the temperature rise)

So if the above was mumbo-jumbo, in plain english: purchasing warmer gasoline results in 1% less gas then what you pay for if it was colder.
At $3 a gallon, you are losing 3 cents worth of gas. Big deal. Of course the implication of this for gas companies is huge since they sell thousands of gallons to consumers.

This math all depends on where the gas tanks are located at the station you fill up at. Often they are located deep underground where temperatures hardly fluctuate because of insulation.