As gas prices continue to skyrocket, are you filling your tank more often in an attempt to save a few bucks (i.e., buy a few gallons today so as not to pay a higher price for more gallons tomorrow)?

Case in point: Last Friday morning a local station was offereing regular gas for $2.799/gal. My tank was full, but I knew the wife's was only about 1/2 full, so when she came home from work at noon we went over there to fill up. In the intervening 90 minutes, the price had increased to $2.869! So instead we filled up a for $.03 less a few blocks away.

 

Not really, no.

Instead I take my time and use the shake and fill method to get as much fuel as possible in. Now, if I know that gas prices are going to skyrocket, I do tend to fill up early, however, it's got to be a big change and I've got to be around a quarter/half tank. Going up a few cents doesn't cut it.

 

I have done it in the past but haven't been doing it recently. This thread spurred my curiosity about how much of a difference it makes so I just broke out the spreasheet and did a quick calculation to see. Here's what I did:

I assumed an initial price of $2.25/gal and a rate of increase of $0.05/week over 27 weeks. I also assumed 200 miles/week on a car that gets 40mpg for a total fuel need of 5gal/week. There are two cars: Car A is fueled weekly with 5 gallons of gas. Car B is fueled every third week with 15 gallons. Here's how it worked out:

Car A: 135 gallons at a total cost of $391.50
Car B: 135 gallons at a total cost of $398.25
Money saved by fueling weekly rather than every third week: $6.75 or 1.7%

**EDIT**
I realized that 200mi/week is a little low so I re-did the calculation for 400mi/week. Car A fuels with 5 gallons twice a week and Car B fuels once every week and a half with 15 gallons. The same rate of increase is assumed, and assumed to be continuous (2.5 cents every half week). Here's how it worked out:

Car A: 270 gallons at a total cost of $779.63
Car B: 270 gallons at a total cost of $786.38
Money saved by fueling twice a week rather than every week and a half: $6.75 or 0.9%

Interesting that the more you drive the less it matters.

 

I fill up 3-6 gallons (quarter to half tank). No real change.

 

I top-off on Friday and Sunday evenings. This lets me track my weekly commute MPG apart from my weekend driving. This allows me to run single variable tests and tweak my driving.

Bob Wilson

 

I always fill up when thegas gauge reads 1, 2, or 3 bars. Then I post my mileage on GH!

 

I read somewhere that in the winter (at least in colder climates), you should keep your tank at least half full all the time to prevent fuel-line freezing.

 

Over the course of last week, prices rose on an average of 11 cents per gallon around Phoenix (so said the local news channel). Even though I had a little more than half a tank, I filled up yesterday. So I voted yes.

I figure, I'll save a few cents by next Friday, when I'd usually be filling up anyways. But if it does go up another 11 cents this week, I'll only have saved 66 cents (or less. I'll probably use up to 6 gallons this week). Only really worth the extra stop because the gas station is across the parking lot from where I work.

 

For a regular, fixed size fuel tank, that is correct. The problem is temperature changes in the winter can result in water vapor condensation in the tank . . . a bad thing. Small planes are always kept fully loaded to avoid the problem since water in the fuel line can make a take-off excessively interesting.

The Prius uses a bladder tank, which keeps out water vapor and contains the gas fumes. Unfortuantely, Prius fuel levels are not terribly precise because of this and the fuel tank capacity can vary. So the good news is very little gasoline vapor ever escapes. The bad news is the actual fuel capacity sometimes varies but not so much a problem . . . more of a quirk.

Bob Wilson

 

I don't but I should. 2 weeks ago ($2.69) I said I should have bought gas 2 weeks ago($2.49)... and I still haven't bought gas ($2.89). When I buy gas next week it'll probably be $3.09 Sigh.