When Should You Fill Your Gas Tank in the Summertime?

You won't save much money. The expansion coefficient of gasoline is 0.000950 per degree Kelvin (or Centigrade),

There’s some truth into that, but not what you’d think. One thing that fuel does, is cool your fuel pump... mechanics usually tell you not to run you tank below 1/4 full. So a full tank in the morning would be better,

Did a quick google search... and sure enough...

I agree with everything said in your referenced piece except, "In modern vehicles, the fuel pump is located within the engine where the fuel helps keep it cool".

Cough, cough, that ain't so. I'm surprised this hasn't been corrected.

Ahh... I didn’t read the whole thing... only to reinforce what I stated earlier...

Correct! I'm sure the author intended to say that the fuel pump was located inside the fuel tank, not inside the engine. A fuel pump inside the engine would be highly subject to vaporlock...

Sorry, I didn't rate that reference highly, being very repetitive and sometimes self-contradictory. "In modern vehicles, the fuel pump is located within the engine" plus "The fuel pump is located in the fuel tank on modern cars" equals confusion between high- and low-pressure fuel pumps.

The 1/4 tank is mentioned, but with no justification as to why it is not 1/8 or 3/8. I have not found this advice in any of my car manuals.

Furthermore the text is almost identical to this site, suggesting the determined circulation of an old wives' tale.

For an entertaining explanation that you should not let the tank go below half-full, see this.

That's fine....

That was not only a quick google search that was the first that appeared... and as far as "In modern vehicles, the fuel pump is located within the engine" plus "The fuel pump is located in the fuel tank on modern cars"

That's already be addressed. More then likely it the quality (lack of) of todays journalism and editors.

Well it depends....it depends on the temperature of the gas, most tanks are well buried so not a lot of temperature variation takes place...It seems that gas pumps in the US are calibrated to 59° F, so if the temperature is above that, then you are getting screwed, however slightly...For every 10.5° C(or 19°F) you lower the temperature, you get a 1% increase in volume....so probably not worth the effort, but it doesn't hurt to be on the right side of the science involved....but I wouldn't go out of my way...

http://datagenetics.com/blog/april32015/index.html

...but then gas pumps are not all that accurate anyway....they are maintained by humans...haha

http://www.sun-sentinel.com/sfl-flhlpgaspump1021nboct21-story.html

"For every 10.5° C(or 19°F) you lower the temperature, you get a 1% increase in volume" [my underlining]

To be clear, that statement needs to be worded more carefully! A decrease in temperature results in a decrease of a given volume of any substance, so a device (eg. calibrated fuel pump) that delivers a constant volume of that substance will deliver a larger mass of the colder material than it would of a warmer material.

I have been amazed to note how cold the delivered fuel nozzle feels, especially on a hot California day... I presume that the fuel is cooled at the refinery to reduce evaporation, and such a large volume of liquid, carried in a shiny stainless steel tank truck, will only warm slowly during delivery from the refinery to the station.

I don't remember what temperature is specified on the local fuel pumps, but I do know that the underground temperature in this area is higher than 59°F. The temperature in my tunnel, whose entrance is both shaded and insulated, varies between about 62°F and 65°F during a year.

The variation in some locales is a little more than that. We have had our water lines freeze up at 13 feet under ground. It goes under a driveway. It wouldn't have happened if it would have had a good snow pack above it.

Based on what I've just found, wholesale transactions of gasoline are temperature compensated while retail sales are not, in the USA, although the technology is readily available and is used throughout Canada.

Thanks to Congress, we're getting screwed here.

The amount of gasoline in a gallon pumped during the summer ...

GROSS vs. NET – When is a gallon not a gallon? | Desert Fuels ...

Still, I'm going to continue to buy fuel when I need it.

well, in Arizona you don't have to worry too much of winter blends... but here are some of the 'unaffordable' solutions... or maybe not...

Gas is sold by the gallon (volume) and not by weight or any other type of value... period.

And each state has a department of weights and measures that do check on the calibration (volume dispensed) of the gas pumps.

Of course it's done in Canada. Here we are colder and the oil companies don't want to get screwed.

I did work for a gas station company for awhile. What I would say for sure is -

"don't purchase gasoline when the tanker truck is filling the underground reservoirs"

Even many hours after the reservoirs are filled, there are suspended particulates in the gas. Not great for any engine, even if you filter most of them out.

As to the temperature / how many gallons are you getting versus the pump - the gas from the tanker will not be at the calibration temperature most times and depending on the season - this will either be in your favor or against you.

Agree with "don't purchase gasoline when the tanker truck is filling the underground reservoirs".

The two brothers who used manage a quick change oil franchise told me, that their dad used to take his gasoline deliveries at night, when the station was closed for the very reason you stated about particulates in the gas.

I drive a Subaru Forester, anybody who owns one of those is not thinking about economy.

The first or last gallon does not matter; it's all coming from the same (probably underground) tank. The temperature in those underground tanks varies only slightly during the day and night. I don't remember seeing a station with above ground tanks in years, and I wouldn't be surprised if they are illegal in Arizona...

Now on the other hand, If you are in the habit of topping off your tank, and do so when the incoming fuel is cold, then don't drive very far before letting the car sit in the sun, there is a very real possibility of the tank overflowing as it warms up. That of course would be wasted money.

The first gallon does matter, sort of. The gas that is trapped in the system near the surface will be warmer, or cooler, than that is in the tank.

That's about the only difference. (Not much)

Cooler gas? How much can it save you?

Can you get more gas/fuel into the tank than it is designed to hold if the fuel is cooler?
I think not!

I also work and live in the deserts of Oman, and asking several folk this morning..... we all have NEVER heard of the "cool gas" theory!

Live and learn I guess!

Here's the problem... There is a misconception that the whole world revolves around the consumer.... well, here's a slap in the face.... it doesn't.

It's not so much how 'How much can it save you?' its about what it can save over all bottom line for the supplier.

Here's an example.

How much would removing (1) olive off of a airline inflight meal save the airline?

Answer: $40,000.00

And this not only how for the oil industry operates, but all business.

Gas tanks?

What is this, the 20th century?

Yes, early in the morning will save you money. You have to beat the store manager raising the price after they come in. There is a particular day of the week in your local area that statistically is the least expensive day at the pump too.

I agree with the tanks buried, they don't vary in temp underground. However, I've heard that filling your tank on the slow flow speed will help save money because at the higher flow rate you get more air bubbles in the stream and you start paying for air instead of fuel.

And just where do these air bubbles originate? If the supply tank is so low that air can get in to the intake of the pump line, then your bigger worry is getting water mixed with your fuel.

It is conceivable that some of the fuel could vaporize into bubbles, but not air bubbles. Whether vapor bubbles would affect the volume of fuel delivered would depend on the design of the volume/flow measuring device, and its location with respect to the pumping device.

If you are referring to air bubbles formed at the exit of the nozzle, that should have zero effect on the volume of fuel measured.

Cavitation. The same as is created by a boat propeller spinning fast underwater creating bubbles.

True cavitation creates vapor bubbles, not air bubbles. Such bubbles collapse very rapidly, and would not be evident at the fuel nozzle. Vapor bubbles would only affect the measured volume if the measuring device was immediately following the hyperactive pump. I do NOT know anything about the current design of dispensing fuel pumps or their measuring devices.

Small boat propellers close to the surface commonly produce a vortex which allows them to entrain (suck in) air bubbles. That is not cavitation.

And if your filling up your car up at the pumps in the morning,... and there's foam coming out of your cars fill tube... Stop immediately.

The only time I fill my tank on anything is when it's low. Seems to be working out.

Possibly the simplest - just empty the loop when you finish. (where applicable)

Old friend used top-up his bike by emptying each pipe at the station.

Regards,

Ex-pump attendant(s).

I've heard that...

I have to confess that I never thought of that! Isn't that theft?

I do notice the "(where applicable)". With the pumps I use, if it is even possible, to do so, I'd have to: 1) stop filling before the tank was full, 2) Return the nozzle to its station to turn off the pump, 3) take the nozzle back out, insert it into the filler, pull the trigger long enough for the hose to drain, and 4) Return the nozzle to its station a second time.

I'm hardly rich by most American standards, but I can afford to pay for the fuel I use!

The best thing to do is, fill your tank before they change the price on Monday.

When you need gas. Seriously the incremental savings you make is not worth the time scheduling, hassles and your personal time value you incur trying to save a dollar or two over the year.

You want to save money on fuel,, buy stock in the oil companies....If you have enough you can break even...

http://www.dividend.com/dividend-stocks/basic-materials/major-integrated-oil-and-gas/

Well maybe start a class action law suit with the Potatoes chip manufacturers you'd have a better chance... lol

Hey Lyn, I say fill it when it needs it regardless of temperature. I hate walking.

So do I.