Gasoline experiment revisited

While using my car for a lot of short trips recently, my gas milage fell below 30 MPG.  This really concerns me because I am still paying nine cents per gallon more than I need to.  I am hoping the MPG will rebound with the change in driving habits back to my regular schedule.  Of course, it could also be damage from the Waldo Canyon fire we had here in Colorado Springs.  Maybe my air filter just needs a good dusting.  I'm going to have to go on line to see where the air filter is and see if I can clean it or replace it on the cheap.

Gas experiment, an epilogue

Just an update on my use of Shell gasoline.  My latest tank was 39.83 MPG, and my continuous average right now is 35.45 MPG.  This is a far cry from my grocery store gasoline range of 30-32 MPG.

Gasoline Experiment, Part 5

Okay.  One month of gasoline testing is completed.  Here are some comparative numbers:

May  = $173.65 total spent, 1561.7 miles traveled, 44.842 gallons used, 34.83 MPG
April = $173.58 total spent, 1489.9 miles traveled, 44.729 gallons used, 33.31 MPG

At first glance, one can see the total spent and the gallons used were almost identical.  That means the average price I paid was very similar for both months ($3.87 in May and $3.88 in April).  However, in May I got 71.8 additional miles and, therefore, 1.52 more miles per gallon.  Had I purchased all my gas at the generic grocery store, I would have bought an additional 2.156 gallons and paid an additional $8.36.

While my experiment did not result in less money out of pocket, it did result in a savings of gallons I did not have to buy.  I also realize there are other variables which were not limited that could have had an impact on my results.  After all, my per-tank MPG ranged from 32 up to 39.  Looking over my old numbers, though, my generic gas MPG ranged from 27 to 35 with monthly averages ranging from 30 to 32.

I am satisfied that buying the more expensive gasoline at Shell is definitely providing me with increased MPG resulting in a small savings over buying the generic grocery store gasoline, and I will continue to believe this until my gas milage drops below 33.

Gas Experiment, Pre-Part 5 notes

Since I started this little gasoline experiment back on May 3, gasoline prices have dropped 15¢, and I have earned a 30¢ discount on the grocery store gasoline.  This discount has to be used before May 31.

Recalculating my original calculations:  If the Shell gas is $3.82 per gallon and I get 35 miles per gallon, that comes to 10.91¢ per mile.  The generic gas is $3.76 per gallon and I get 32 miles per gallon, that comes to 11.75¢ per mile.  I would save 0.84¢ per mile by buying the more expensive gas.  I drive about 330 miles per week to work, so I would save $2.77 per week on gas.

Now, calculating the 30¢ discount, my generic gas would be $3.49 per gallon or 10.9¢ per mile.  Is this worth polluting my gas tank for?

Gas Experiment, Part 4

The last 2 tanks of Shell continue to vary but show improvement over the generic gas.  One was 34.77 MPG, and the other was 36.27 MPG.  The odd thing is the 36.27 was because of 3 more miles but 0.12 gallons less.  That little bit of shift created an increase of 1.5 MPG.

Gasoline Experiment, Part 3

That's more like it.  For my latest tank of gas, I got 36.96 miles per gallon using Shell gas instead of the generic grocery store brand.  Just to make sure this is not a fluke, I checked all of my MPGs for as far back as I could go.  This revealed some striking numbers.  I did, indeed, have some previous tanks of gas as high as 35.99 MPG.  However, my records do not indicate where I purchased the gas.  My monthly average MPG, though, indicate 30 MPG during the cold months and 32-33 MPG during the warm months.  Therefore, a monthly average over 33.66 MPG should prove the Shell gas is a causal factor.  I guess this means my next gasoline post will be at the beginning of next month.

Gasoline Experiment, Part 2

Okay.  Just filled my tank again.  The news is not encouraging.  The MPG this time around was only 33.56.  A bit disappointing compared to what Shell gas did for my car last time.  Well, we shall see how this second tank comes out before making any decisions.  After all, when I had 2 tanks of Shell followed by 1 of generic, I got 39 MPG.

Seeing the $23 spent for a tank of gas, however, made me think.  At what price is the Shell gas really a frugal purchase?  To figure this out, I came up with this formula.  Generic bill calculation:  165 miles ÷ 32 MPG = 5.156 gallons of gas; 5.156 gallons x $3.869 per gallon = $19.95 total bill.  Shell price per gallon calculation:  165 miles ÷ 35 MPG = 4.714 gallons of gas; 4.714 gallons x ? per gallon = $19.95 total bill or ? per gallon = $19.95 total ÷ 4.714 gallons = $4.232 per gallon.

Is that mathematically correct?  Let's see, 4.714 gallons x $3.949 = $18.62.  Therefore, at 35 MPG I would pay $18.62 total at shell, but at 32 MPG I would pay $19.95 at the grocery store.  As long as I am getting 35 MPG, I there can be a price difference per gallon of 36.3¢ per gallon.

Using the same formulas, can I figure out how much MPG I need using Shell gas?  $19.95 total ÷ $3.949 per gallon = 5.052 gallons; 165 miles ÷ ? MPG = 5.052 gallons or ? MPG = 165 ÷ 5.052 = 32.66 MPG.  As long as I get 0.66 more MPG using the Shell gas, I should be saving money.

So why did the $23.01 today seem so high?  Had I bought the gas at the generic price, it would have cost me 5.826 gallons x $3.869 per gallon = $22.54.  However, using the generic gas would have been 32 MPG, and I would have needed to buy more gallons (195.5 ÷ 32 = 6.109 gallons x $3.869 per gallon = $23.64).

If all of these numbers are correct, I need to get at least 0.66 MPG more at an 8¢ price difference to make the Shell gas a frugal buy.  If I do, indeed, get 35 MPG using Shell, the price difference can be as high as 36.3¢.  In 3 days, I will buy another tank, and we shall see if these numbers hold up.

Gasoline Experiment, Part 1

It figures.  Last night I bought the Shell gasoline.  When I get back home, the grocery store generic price came down 2¢ per gallon.  Recalculating from the last time, that means generic gas is $3.86 per gallon and I get 32 miles per gallon, that comes to 12.09¢ per mile.  I would save 0.72¢ per mile by buying the more expensive gas.  With an 11¢ price difference between gas types, I am still saving money if my gas milage remains at 35 with the Shell gas.

The last tank of gas I bought got me 33.49 miles per gallon.  This is with a couple tanks of grocery generic gas after a few tanks of Shell.  Last night, I bought the Shell gas again.  I should have my first new figures on Tuesday morning.  I can say my car seems to like the Shell.  There is less warm-up time after ignition.  Also, the gas gauge seems to be moving slower than usual, so that is a good sign that this will work.  I am keeping my fingers crossed.  If I can save another $10 a month by buying a more efficient gas, I am closer to my goal and maybe won't have to move or become homeless.  We shall see.