Pump Gas In The Morning To Save Money? Nah.

Consumer Reports wants you to know that it’s OK to sleep in, because you’re not going to save money by pumping gas in the early morning. Why not?

The basic facts are correct, but the advice is not. Gasoline does expand and contract a little depending on its temperature. When gasoline rises from 60 to 75 degrees F, for instance, it increases in volume by 1 percent while the energy content remains the same.

But filling stations typically store their gasoline in underground tanks, where the temperature variation during the day is much less than in the air above. The result is that the temperature of the gasoline coming out of the fuel nozzle varies very little, if at all, during any 24-hour stretch at any particular station.

CR did some temperature testing at their auto test facility where they have an underground fuel tank similar to the ones that gas stations use. Here’s what they found:

While the air temperature between filling varied by up to 12 degrees, the fuel in our underground tank stayed at a steady 62 degrees F. As a result, we found that after the first few gallons were pumped, the fuel temperature coming out of the nozzle varied very little between morning and afternoon.

Like a hose sitting in the sun, gasoline that was sitting in a pump and not being dispensed tended to warm up– but those few gallons didn’t make much of a difference. Ultimately, CR found that there was no reason to pump in the morning.

Even with the temperature swings we saw in the first few gallons pumped at our facility, we didn’t see a big penalty for the consumer. A 15-degree difference, for example, would result in a one-percent gain in volume. Or, just a few cents difference on the first gallons pumped—not enough to change your schedule or routine in chasing costs, especially if it might increase your fuel consumption in the pursuit.

You can get the rest of the details of their testing by clicking here.

Save on gas with morning fill-ups? Don’t bet on it [CR]
(Photo: Listener42 )


Edit Your Comment

  1. wgrune says:

    Now people just need to quit passing on those ridiculous chain emails and believe this report.

  2. roshambo says:

    I take chain emails “very seriously”

  3. illtron says:

    @wgrune: Any time I get one of those ridiculous emails pushing some stupid scheme like this, or some missing child, or horrible political manifesto, I immediately reply with the appropriate Snopes page, because nine times out of 10, Snopes is one step ahead of me.


  4. dako81 says:

    @wgrune: Sadly, I don’t think that will ever end. It will just subside for awhile then come back, like a wave.

  5. shepd says:

    If the pump is actually dispensing a different amount when ambient temperature changes, in most places this indicates the pump is faulty and the owner should be informed. Repeated violations should be reported to your authorities. It is illegal in most places to dispense gasoline/diesel without the pumps self-correcting for volume / temperature.

  6. ViperBorg says:

    @dako81: You and me both.

  7. @ Illtron

    I’ve been doing that for years as well.

    Nothing stops friends and family from including you on these things faster than a Reply-To-All with a “Helpful” snopes.com link that helps the person realize “I just spammed all my contacts with trash”.

  8. trixrabbit says:

    here’s something interesting to read:

  9. Farquar says:

    Meg, didn’t you already do this article?


    I think I recall that Jalopnik also did an article encouraging half of the debunked myths.


  10. balthisar says:

    Ah, finally an authoritative source. I’ve been preaching this for a couple of years now, but everyone thinks I’m either crazy or don’t know a lick about the most basic science.

  11. TVarmy says:

    Why not just sell gas based on weight? I mean, it’s all chemistry anyway, matching 14.7 molecules of air to 1 molecule of gasoline. The transition would be a great time for the oil companies to raise prices in the confusion.

  12. TVarmy says:

    @Farquar: People tend to fall for the same myths over and over. Every time gas goes up even a nickel, that old chain letter about not buying gas on days with a “T” goes around, claiming it will get the oil companies to drop prices dramatically.

  13. Jean-Baptiste Emanuel Zorg says:


    It is illegal in most places to dispense gasoline/diesel without the pumps self-correcting for volume / temperature.

    You are correct when you say a fuel pump that dispenses different amounts when the ambient temperature is different is faulty, but not for this reason. It’s because the ambient temperature has nothing to do with the volume dispensed, not because of any temperature compensation mechanism in the pump.

    Fuel pumps in the US are not temperature compensated.

  14. xkaluv says:

    Sounds like a job for the Mythbusters.


  15. Canino says:

    So I can’t save money by filling up early? Dang.

    Thank goodness I aired up my tires yesterday.

  16. iMe2 says:

    What is this “morning” you speak of?

  17. doctor_cos wants you to remain calm says:

    @Canino: Putting air in your tires, you should do in the morning. Seriously. Before you drive around too much.

  18. stevegoz says:

    I saved nearly a buck today by filling up in the morning. Paid $3.87/gallon just before 11 am; as I was leaving the gas station the digital pricing board had changed to $3.95!

  19. CRSpartan01 says:

    @TVarmy: Kinda like how the IOC redid the gymnastics scales so no one really knows what’s going on anymore??

  20. Chairman-Meow says:

    @illtron: Make it more entertaining by hitting reply-all instead of reply when sending them to Snopes :-D

    Shame sometimes works wonders on people.

  21. Keen314 says:

    @shepd: The volume is the same, it’s only the density that’s changing.

  22. Radoman says:

    “While the air temperature between filling varied by up to 12 degrees……”

    I’m not sure if you can save money with morning fill ups (other than stevegoz’s proven method), but I am sure that a majority of the country could do a much greater swing in temperature than 12 degrees between morning and noon.

    Just seems a bit glib..

  23. zero2dash says:

    Quiktrip always changes their prices in the morning; around 9-10am CST. I go there around 7:45am, I can (for example) pay $3.50. On the drive home, I pass the same Quiktrip and notice the gas is $3.60+.

    It’s happened way too many times.

    The temperature may not have anything to do with it, but around me – they do change their prices mid-morning (usually raising them, not lowering them). That’s been my experience at least. Quiktrip does it first, then all the other gas stations change their prices as well.

  24. synergy says:

    They should pump gas at 4PM in south Texas. It’s not the temperature of the gas at the station that’s the issue here, but the temp of the gas in your tank. If you open the gas cap you will hear a long hiss and smell the gasoline. If not to save a penny or however much that was that just evaporated into the air out of your tank, at least don’t screw up the environment by releasing those fumes into the air in the middle of the hot afternoon. My opinion anyway…

  25. CyberCowboy says:

    One thing I’d like them to check on, because I’m not sure I’d know how to check it myself is AFTER it leaves the nozzle, how much evaporation happens while the cap is off the tank, I doubt it’d make a difference, but this is one I’ve been hearing lately but don’t know how to fight it.

  26. I kid you guys not, true story:

    A co-worker came up to me and said that she had to share her trick to saving money on gas, that it was cutting the amount she spent on gas in half. Her trick? Only let it get half empty before filling up again. I asked her how often does she fill up now with her new trick. She said twice a week. I asked her how often she filled up before implementing her new trick. She said once a week. I paused to let that sink in, but it didn’t. So I pointed out to her that she really isn’t saving money, just spreading it out over two purchases. She thought about it for a moment, then got mad at me for “ruining” it for her.

  27. mike says:

    I always wondered how stuff like this gets into people’s heads. There used to be a facebook group that wanted to do a boycott of buying gas for one day. They’re thinking is if everyone didn’t buy one day that gas would become much cheaper.

    Anyone versed in economics (hell, common sense!) would know that this doesn’t work. But people still believed it.

    It just amazes me the things people will believe.

  28. mike says:

    @FightOnTrojans: Actually, this isn’t a bad “trick” because it works on two levels.

    Economically, if your purchasing gas before you become “desparate” for gas, you can shop around a bit. Since you don’t have the urgant need, you won’t feel the pressure to pay as much.

    Psychologically, it makes you feel better because it seems like you’re not paying as much. Consumer confidence is important. And consumer confidence is very much a psychology.

  29. badgeman46 says:

    I am always shocked how much press this myth gets, even on CNN, they say that you should fill up when its cold. As a former gas station employee, I can tell you that the printout from the tanks rarely varied more that a couple degrees. The inground tanks were almost always a constant 55 degrees. The only time it would change is when we got a delivery, which makes sense, as it is coming from a warm tanker.

  30. ratnerstar says:


    Why not just sell gas based on weight?

    But what if I want to buy gas in space?

  31. crashfrog says:

    @linus: Shop around where? In 30 years I’ve never lived anywhere where the gas stations didn’t all have the exact same price.

    Sure, maybe the next city over there’s a 3-cent difference. Irrelevant, since it costs more in gas to get over there and back.

    No price-fixing, though. Free market!

  32. Brunette Bookworm says:

    @crashfrog: Not exactly price fixing since you’ll see one station change first, but if one goes down, the others change their prices, too. They know everyone will go to the cheaper station if they don’t. If it goes up, other stations start to go up, too. Some will hold out, if they are smaller, but why lose money when you can increase it? It’s like any item, stores in an area try to match their prices to one another on items like movies, groceries, etc. They send people to see what the prices are and will change theirs accordingly.

  33. temporaryerror says:

    If you live on the border between two states, often times the price in one state will be noticeably cheaper than in the other state.

  34. nsv says:

    @crashfrog: I passed several gas stations today. Each had a different price. The cheapest was 12 cents less than the most expensive.

  35. neko613 says:

    When it’s almost 100 degrees in Cali, I can assure you that the underground tanks get hot too. The freaking black tarmac could give bare hands burns on a hot summer day.

  36. crashfrog says:

    @mjane79: But the grocery stores don’t do that. Steaks that are 5.99 a pound at HyVee might be 6.59 at Russ’s, or 5.29 if they’re on sale.

    But gas, for some reason (hint hint) is different – it’s never on sale, it’s never cheaper with a coupon, it’s never more expensive at the upscale gas station that serves you free coffee while they pump it for you. For everything else, there’s a continuum of prices that reflect the region you’re in, the level of service the establishment tries to offer, their capacity to leverage buying power, and a dozen other individual factors that lead to different outfits offering different prices.

    And yet, in a minor city of around a quarter-million people, all the gas stations have exactly the same price. Free market! Please.

  37. zolielo says:

    @linus: About multiple fuel stops per week over minimal fuel stops per week.

    It is generally better to fill once per week instead of two or more times. (Or whatever multiple fuel stops per week over minimal fuel stops per week.)

    The reason being that gasoline does add weight to the vehicle. Running down the tank reduces weight which leads to greater fuel economy (mpg full tank < mpg less than full tank).

  38. @badgeman46: @linus: A Nissian dealer near me has been adding this into their commercials as a way to save gas. I heard it this morning while listening to the OPie and Anthony show.

  39. balthisar says:

    @neko613: How do they get hot? They’re geothermally cooled.

  40. Meathamper says:

    Oh I’m sorry, is Consumer Reports the new Mythbusters?

  41. chirag says:

    @neko613: Nah! the underground tank should be much cooler than the surface temp. In India in some places people are experimenting with geothermal cooling for houses using this principle with water, several hundred feet of pipes and a circulation system. apparently you save quite a bit on electricity using this trick.