Home > New Challenge: Pump Gas In the AM Only

New Challenge: Pump Gas In the AM Only

June 24th, 2008 at 11:37 pm

I find it much easier to take money-saving steps when the payoff is readily apparent:

- Clip a coupon, save a buck at the grocery store.
- Take a defensive driving course, save 10% on my car insurance.

Where it's more challenging is when the payoff amount isn't really known, I just know that I'm saving "something." And if you throw in the fact that taking a particular step to save money is something I think of as a bit unpleasant, then it gets really hard to get and stay motivated to do what I know I should.

Those are the times when this blog really helps, because accountability comes in to play. And it seems "challenges" appeal to my competitive nature and help me stay interested.

Back in late-January when I was pondering our electric bill, I came up with a "Steam Free Mirror Challenge" for myself:

Text is and Link is

I am proud to say that except for one day when I was having a bit of rough morning and decided a steamy shower would be good therapy, every morning since starting the challenge my mirror has been steam free!
I know I'm saving on my electric bill, but I have no idea how much. My "payoff" is getting to brag here!

And now I have a new challenge for myself that I came up with while thinking about the rising price of gas: to only pump gas in the morning!

I know pumping gas in the morning when it is cooler (and therefore the gas is denser) can save you money (Edit note: I edited this from "quite a bit of money" to just "money" ... please see comments below). And I live in a hot place where the difference in temperature between the am and the pm can be 30 degrees. I know I should pump my gas in the morning. Problem is, I am not a morning person.
In order to pump gas in the morning on my way to work instead of on my way home from work, I am going to have to get my lazy self out of bed 15 minutes earlier.

I guess that's why it's called a challenge, eh?

EDIT - Additional comment: I'm also thinking about letting my tank get lower between fill ups, just so I'm dragging less weight (gasoline in the tank) around to improve gas mileage. After going through a 5-day widespread power outage and being unable to buy gas without driving over 30 minutes and waiting in line, I started filling up somewhere between 1/2 and 1/4 full. But I'm thinking maybe I should go back to waiting until it gets below 1/4 full to refill. Does anyone have an opinion on this?

10 Responses to “New Challenge: Pump Gas In the AM Only”

  1. Lady T Says:

    Wow, I did NOT know that! I will have to challenge myself to pump gas only in the AM also, because I am not a morning person either and always fill my tank in the evenings ... and I live in Texas also (Ft. Worth) so I definitely know about those differences in temps between the morning and the evening!!

  2. glock35ipsc Says:

    If you are not a morning person, you are better off staying in bed then! LOL! 99% of the gas at gas stations are stored in underground tanks, therefor the temperature of the fuel is cool and consistent. The only time the fuel would be at a temperature to make a difference is right after the fuel has been delivered, likely to be warm from being in the truck's tank. Regardless of ambient temperature, the fuel temperature in the ground will remain cool and consistent, and there is not enough time between leaving the tank, routing through the pump and through the hose to raise the temp to that of one that will make any difference.

    The practice of pumping fuel in the mornings due to the fuel's "density" is easily debunked, and is one of those myths that after it is told enough times, it eventually becomes fact.

  3. scfr Says:

    glock35pisc - Do you own a gas station by any chance? If so, I understand why you wouldn't want me to save 1% on my gas bill by pumping gas in the morning. For me, 1% (and surely more than that in a Texas summer) is worth it!
    Text is and Link is

  4. glock35ipsc Says:

    Nope, I just do the science and math. I/my family has been in the excavating business long enough to know that ambient temperature changes over a 12-14 hour period will not change to temperature underground at 3-15 feet below the surface.

  5. scfr Says:

    I first heard this money saving tip on NPR over a year ago. Since then, I also read about it in the paper. I consider those to be reliable sources, as well as Snopes. I don't know if they are always right, but I do consider them reliable. I have not heard or read from a reliable media source that pumping gas in the AM will not save me money; at worst, I have heard that the savings will be minimal. Minimal savings work for me. Remember, there are many of us here who stop to pick up pennies off of the ground. For some it is worth the effort, for some it is not. For me, it is.

    But, if I get tired of waking up earlier (2 mornings a month) to fill my tank I may use this as a fall-back excuse, so thanks!

  6. JanH Says:

    I think that our news might have had that on at one time. I know I've seen it somewhere. It gets so HOT here with heat indexes and often doesn't cool down at night. Around 80 degrees at night in the deep part of summer. It couldn't hurt to try it here.

  7. merch Says:


    I agree with Glock. It's a myth. Consumer Reprots also says it's a myth. And there are other ways to save money on gas.

  8. merch Says:

    The best way to burn less fuel is to buy a car that gets better gas mileage. But our tests with a Toyota Camry and other vehicles show there are ways to minimize what you spend at the pump with your current car.

    Drive at a moderate speed. This is the biggest factor. You may have to be a little patient, but driving at 55 mph instead of 65 or 75 will save you money. When we increased the Camry's highway cruising speed from 55 mph to 65, the car's fuel economy dropped from 40 mpg to 35. Speeding up to 75 mph cost the car another 5 mpg. One reason is that aerodynamic drag increases exponentially the faster you drive; it simply takes more fuel to power the car through the air.

    Drive smoothly. Avoid hard acceleration and braking whenever possible. In our tests, frequent bursts of acceleration and braking reduced the Camry's mileage by 2 to 3 mpg. Once up to speed on the highway, maintain a steady pace in top gear. Smooth acceleration, cornering, and braking also extend the life of the engine, transmission, brakes, and tires.

    Reduce unnecessary drag. At highway speeds, more than 50 percent of engine power goes to overcoming aerodynamic drag. So don't carry things on top of your vehicle when you don't have to. Installing a large Thule Cascade 1700 car-top carrier on our Camry dropped its gas mileage from 35 mpg to 29 at 65 mph. Even driving with empty racks on the car reduces its fuel economy.

    Don't use premium fuel if you don't have to. If your car specifies regular fuel, don't buy premium under the mistaken belief that your engine will run better. The only difference you'll see is about 20 cents more per gallon. Most cars are designed to run just fine on regular gasoline. Even many cars for which premium is recommended will run well on regular. We have found that the differences are imperceptible during normal driving. Check your owner's manual to find out if your engine really requires premium or if you can run on other grades.

    Minimize driving with a cold engine. Engines run most efficiently when they're warm. In our city-driving tests, making multiple short trips and starting the engine from cold each time reduced fuel economy by almost 4 mpg. Engines also produce more pollution and wear faster when they're cold. When possible, combine several short trips into one so that the engine stays warm.

    Keep tires properly inflated. The Camry experienced a 1.3 mpg loss in highway fuel economy when the tires were underinflated by 10 psi. More important, underinflated tires compromise handling and braking, and wear faster. And they run much hotter, which can lead to tire failure. Check the pressure of your vehicle's tires at least once a month with a tire gauge. The owner's manual explains how to do it.

    Buy tires with lower rolling resistance. A tire's rolling resistance can add or detract another 1 or 2 mpg. In our tire ratings, look for high-rated tires with low rolling resistance. They generally won't cost more, and replacing a worn tire could save you more than $100 a year in fuel.

    Avoid idling for long periods. Think of it this way: When you're idling, your car is getting zero miles per gallon. When we let a Buick Lucerne, with a V8, idle for 10 minutes while warming up, it burned about an eighth of a gallon of gas. A smaller engine would probably burn less, but idling still adds up over time. As a rule, turn off your engine if you expect to sit for more than about 30 seconds. An engine warms up faster as it's driven anyway.

    For more information on saving fuel and alternative fuel vehicles, see our Green car guide.


    Morning fill-ups. A common tip is to buy gasoline in the morning, when the air is cool, rather than in the heat of the day. The theory is that the cooler gasoline will be denser, so you will get more for your money. But the temperature of the gasoline coming out of the fuel nozzle changes very little, if at all, during any 24-hour stretch. Any extra gas you get will be negligible.

    Air conditioning vs. opening windows. Some people advise you not to run the air conditioner because it puts more of a load on the engine, which can decrease fuel economy. But others say that opening the windows at highway speeds can affect gas mileage even more by disrupting the vehicle's aerodynamics. Our tests show that neither makes enough of a difference to worry about. Using air conditioning while driving at 65 mph reduced the Camry's gas mileage by about 1 mpg. The effect of opening the windows at 65 mph was not even measurable.

    A dirty air filter. Our tests show that driving with a dirty air filter no longer has any impact on fuel economy, as it did with older engines. That's because modern engines use computers to precisely control the air/fuel ratio, depending on the amount of air coming in through the filter. Reducing airflow causes the engine to automatically reduce the amount of fuel being used. Fuel economy didn't change, but the Camry accelerated much more slowly with a dirty filter.

  9. simpletron Says:

    one of reason why geothermal heat pumps are so efficient is because below the frostline, the temperature of ground does't really change much. gas tank are buried below the frostline.

    the only amount of fuel that is affected by the change in air temperature is the fuel in the pump itself which amount to less than a gallon. given the thermal expansion of gasoline, a 10C(18F) change in the fuel temp amounts to about 1% change in volume. on a 10 gallon fillup, at worse you would spend .2% more or about 8 cents. i say at worse because to realize a 20C(36F) change in the temperature of the gas in the pump would take a couple of hours of no use on a very hot day(100+). also the night temperature would also have to be at least 20C(36F)cooler than during the day.

    a funny consequence of this is that if you are the first person to use the pump in the morning then you will spend more than a person that fills up right after someone during the hottest part of the day. this only works in the summer when the night temperature is warmer than the ground temperature.

  10. scfr Says:

    Quote: Any extra gas you get will be negligible.

    I'll take negligible! I wonder if, with rising fuel prices, CR's thinking on this will change? Think about how many people who could't be bothered with coupons in the past are now starting to clip them due to rising grocery prices.

    The other tips we already follow (except I do turn on the A/C when it gets over 90). The pumping gas in the AM is the last one to be adopted because it requires the most discomfort (having to wake up earlier).

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