Fill fuel in the coolest hour
 

They say fill fuel in the coolest hour? Why and How it improves /impacts the car?

Negligible difference at best. Much like when people say their car is special and gets it's best mileage at 9 million mph.

The idea is the fuel is more dense and so you get more energy per gallon being paid for. The problem is that liquids don't change volume much due to temperature. There is far more variability/inaccuracy in the meter on the pump.

While the difference is small, it is not entirely negligible.

https://www.quora.com/How-much-more-dense-is-gasoline-in-50-degree-F-weather-than-it-is-in-80-degree-weather
https://qph.ec.quoracdn.net/main-qim...80c428996.webp

Seems like 1% for every 8 degrees Celsius.
At least there's some compensation for winter gas being less dense.

Looking up the prices at https://www.eia.gov/petroleum/gasdiesel/ $2.50 seems average in most states.
Let's say with ten gallon at $2.50 a gallon then a hot summer afternoon or chilly morning at 16 degrees less could make a 50 cent difference for the same fuel.
Or get you 0.2 gallon extra for free; that's 12 whole miles at 60 mpg...

When it is cold and you don't plan on driving much after fillup, don't brim it to the neck; it might spill when it expands.

Here in the Netherlands gas goes for €1.66 a liter, that would be about $7.50 a gallon... But most of our filling stations have underground gas tanks and therefore hardly any temperature variation.

Since the gas station's tanks are likely underground, the weather at the moment won't affect the volume until it's already passed through the pump's meter.

If you're referring to my statement about the meter, then I will ask; how accurate do you think the meter is?

If there is such a difference in volume depending on temperature, wouldn't the retailer use temperature correction when metering? (I don't know what answer)

I got 50+ mpg for a long time with one pump. Deleted most of those fills. Thought a co-worker was messing with me at first. Then he started using that pump to.

It was only one fuel on a pump with 4 that gave bonus. I'm guess the inspector doesn't check every fuel at every pump.

Around the world airplane's filled their tanks with COLD fuel becasue it was DENSER (more fuel per voulume), so that later when it warmed and expanded they had more fuel to burn:

Ala' -- 11 pounds of fuel in a 10 pound bag!

My favorite is the idiots who claim their car "gets xx mpg no matter how I drive it, all day long." Like, yes--your car, unlike every other car in the world, is not subject to the laws of physics or thermodynamics, and your "results" aren't simply an indicator of your poor record-keeping and observational skills.

This article from how Stuff Works claims fuel meters are temperature-corrected by the pump computer, but doesn't say anything else about it. I've found some sources online that say temperature correction is required in the EU and Canada. Edit: In the UK and Canada, Automatic Temperature Correction is required at gas pumps. The Wikipedia article on fuel dispensers says,

"There are far fewer retail outlets for gasoline in the United States today than there were in 1980. Larger outlets sell gasoline rapidly, as much as 30,000 US gal (110,000 L) in a single day, even in remote places. Most finished product gasoline is delivered in 8,000- to 16,000-gallon tank trucks, so two deliveries in a 24-hour period is common. The belief is that the gasoline spends so little time in the retail sales system that its temperature at the point of sale does not vary significantly from winter to summer or by region."

With no citation, of course, so who knows?

Like Charlie mentions, the fuel is stored underground, so it doesn't matter what the outside temperature is, the fuel is dispensed at virtually the same temperature; fuel density vs. temperature is moot.