[doganjo]

Just got this in an email from a friend

SAVE MONEY on fuel
Only  buy or fill up your car or truck
in the early  morning when the ground temperature is still  cold.
Remember  that all service stations have their storage  tanks buried below ground. The colder the ground  the more dense the petrol, when it gets warmer  petrol expands, so buying in the afternoon or in  the evening....your litre is not exactly a  litre. In the petroleum business, the specific  gravity and the temperature of the petrol, diesel and jet fuel, ethanol and other petroleum  products plays an
important role. A  1-degree rise in temperature is a
big deal for  this business. But the service stations do not  have temperature compensation at the  pumps.
When  you're filling up do not squeeze the trigger of  the nozzle to a fast mode  If you look you will see
that the trigger has  three (3) stages: low, middle, and high. You should be pumping on low mode, thereby  minimizing the vapours that are created while  you are pumping. All hoses at the pump have a vapour return. If you are pumping on the fast  rate, some of the liquid that goes to your tank  becomes vapour. Those vapours are being sucked  up and back into the underground storage tank so  you're
getting less worth for your  money. One  of the most important tips is to fill up when  your Petrol tank is HALF FULL. The reason  for this is the more Petrol you have in your  tank the less air occupying its empty space.  Petrol evaporates faster than you can imagine.  Petrol storage tanks have an internal floating  roof. This roof serves as zero clearance between  the Petrol and the atmosphere, so it minimizes the evaporation. Unlike service stations, here  where I work, every truck that we load is  temperature compensated so that every litre is actually the exact amount. One last tip, if there is a petrol truck pumping  into the storage tanks when you stop to buy
Petrol, DO NOT fill up; most likely  the petrol is being stirred up as the Petrol is  being delivered, and you might pick up some of  the dirt that normally settles on the  bottom.

[robert waddell]

it all relates to petrol  NOT diesel
will the ground temp rise that much in Scotland in an 8 hour period
weights and messures will have a field day with all the petrol stations shorting there customers
i think it is common policy for petrol stations to close when they are refilling the tanks      health and safety issues
tesco had an issue with water in there petrol but that was a good while ago      they also had diesel in there petrol as well 

[doganjo]

In the petroleum business, the specific  gravity and the temperature of the petrol, diesel and jet fuel, ethanol and other petroleum  products plays an
important role. A  1-degree rise in temperature is a
big deal for  this business. But the service stations do not  have temperature compensation at the  pumps.

it refers to ALL fuel, Robert. And yes, the temperature does vary that much - at Morrisons here yesterday it was plus 9.5, the night before it was zero.  I don't think Weights & Measures would be interested as the amounts would be variable and minimal, but it would make a difference to the motorist if he got enough fuel extra to get that last 3 miles home!
Is there a reason you are dissing this?  It seemed sensible advice to me.

[Plantoid]

Check it out on Snopes urban myths

Seeing as the main tank is below ground and will have a few hundred or so gallons in it at refill time all at the below ground temp I doubt you will get any advantage .. the metering .... weights and measure guys would also have a bit to say if there were difference of a percent or so  in the deliveries to the vehicle .

 Here in the UK the tanks are also pumped from the bottom fairly often to remove excess water and crud in the tanks .. fuel is allowed a percentage of water for the warmer moist air above ground condenses out in the tank when fuel is being pumped into vehicles .

 Like Robert said , you may get contamination between tanks and with excess water on some of the older tanks where the measuring rod was about six inches longer than the depth of plunge .
Some times it used to oscillate as the tank was being filled and slowly sctatched  a hole in the bottom of the tank or on the older rusting tankl the action of dropping the rod down the tube and it hitting the bottom pierced a hole in the bottom of the tank .

 Our local Coop garage got done for environmental pollution about four years ago for not sussing that this had happened to their diesel tanks .  Apparently so for over three years during which time a 1/4 inch slick of diesel regularly  covered a local stream a few hours after it rained hard .  They must have not had any decent reconcillation  system in place for fuel in and fuel out costings /sales.

They now have had all tanks replaced  and also  paid for a massive clean up of the trout / salmon  feeder stream at Crosshands.

[robert waddell]

Annie not dissing it at all  why do you mention that anyway
i think plantoids responce supports what i did write
also the safe use and storage of fuel has been well documented in tractor instruction books since the fifty's and can remember the fuel deliveries with measured containers (big jugs)          so it appears old hat to me
on the temp debate with the figures you have quoted   you have not allowed for the tank being 10 to 15 feet in the ground even -20 does not penetrate to two and a half feet  Canada yes but not Brittani and the heat source ground pumps derive heat from the ground      has anybody taken a temp reading at the bottom of the storage tanks and the top  and the fuel delivered and the air temp
there is a huge difference betwean petrol and diesel    petrol vaporises diesel does not unless it is subjected to very high pressure
or am i dissing you with information

[bazzais]

They fill planes by weight of fuel and not by volume - the same as an F1 car.

Ta

Baz

[Victorian Farmer]

i always let the engine warm up on tic over

[Womble]

Thanks for posting - it does us all well to think about these things once in a while. However, just because I'm sitting at a computer with a physical properties database on it  :

                                      0 degC,      +10 degC    +20 degC
Petrol Density, kg/m3       763               754.3         745.5
Diesel Density, kg/m3      856.9             843.2        836.3             

So that gives a density difference of *roughly* 1.2% for petrol, and 0.8% for diesel for a 10 degC temperature rise. So I guess for a £50 fill of your tank, you might theoretically save £60p. However, i'd have thought it's highly unlikely that the temperature of an underground storage varies by anywhere near that much over the course of a day, so in practice, I shouldn't think it's worth losing much sleep over.

The thing about filling up when half full is a bit strange though, as that means that you're always carting half a tank's worth of petrol around with you that you never use, and I'm sure that will have just as big an impact as any vapour generation!

Actually, the thing that makes the biggest difference is how you drive, how fast you drive, the roofrack you left on, and how much cr@p you keep in your boot!! 

[doganjo]

Well I am not a scientist, nor a motor mechanic, nor a whiz kid with computers, and I don't believe everything I read, but neither do I disbelieve everything I read or am told, so it made me think about how I use my fuel and whether I should do things differently.   By the looks of it, it made some of you think too.  Mission accomplished I think!

[SallyintNorth]

Well I am not a scientist, nor a motor mechanic, nor a whiz kid with computers, and I don't believe everything I read, but neither do I disbelieve everything I read or am told, so it made me think about how I use my fuel and whether I should do things differently.   By the looks of it, it made some of you think too.  Mission accomplished I think!

Good one Annie