Why do they say you shouldn't fill up your car in the daytime?

Not necessarily a rule.

Gasoline expands during the heat of the day and one receives less than the pump records.

It contracts during cooler times and one may receive more.
Nights and winter.
The US gov. is looking into this and contemplating a requirement that pumps be maintain at a constant temperature.
How much? Who knows? The "Shadow" of gov. knows.

The only other consideration is when a station is receiving a shipment. As it is being poured into the underground tanks, any sediments are stirred up and one will pump that into their tank. The sediment settles in a short time.

truly speaking

fill your car up in the morning because everything is alot cooler and by that I mean the gas, the underground tanks, just the weather overall. The cooler something is the tighter and more dense the molecules are which means you'll actually get more gas for your buck if you fill up when it's cooler in the morning.

The Mr. Pine

They don't say that around here and it makes no difference to me.

todvango

It's to help minimize the creation of ground level ozone, which can be bad for our health. The idea, although I don't know if I fully subscribe to this, is that we can all do are part to reduce ozone emissions, particularly on days where ground level ozone is already shown to be high due to weather and localized environmental conditions. On "ozone action days", they recommend the public TRY to adhere to the following...

http://www.setrpc.org/index.php?option=content&task=view&id=124

If you follow that link, you'll see items 5 and 6 are...

- Try to wait until late in the day to refuel your vehicle. The vapors that escape into the air bake in the heat and can add to ground-level ozone formation.

- Don't top off your gas tank when refueling. Avoid spilling gas when you are at the fuel pump.

So there it is. But I have to be honest, I drive for a large portion of my job, when that tank hits E, I have to fill up, it doesn't make much difference what time of day it is.

(Steph basically had it right, but everyone wanted to give her thumbs down...)

For more information, do a search on "ozone action days".

sensible_man

Many people think that expansion will make your tank seem full when it's not or that the pressure caused by the heat of day will expand the gas too much. Think about it though, the gas will be in the tank the next day so it makes no difference. Newer cars have unvented gas tanks, thats why you hear the "whoosh" when you uncap it.

cgriffin1972

Pure stupidity.

it makes no difference - the gas pump is going to give you whatever you pump so it is not true

â™¥â™¥The Queen Has Spokenâ™¥â™¥

My husbands theory is that during the heat of the day in summer the gas expands and you actually get less than if you fill during the cool of th evening when the gas has had time to return to "normal" How true I don't know, except he did work in the oil field... so maybe there was something that was of those behind the scenes things that is not told to the public.

CHRIS M. IS THE WALRUS!

Dunno...

DennistheMenace

Who said that?

â™¥Stephanieâ™¥

Because its bad for the environment. They dont want anymore fumes released during the day

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