Fuel saver e-mail doing the rounds... -------------------------------------------------------------------------------- Thought this might be of interest. Tips on filling your car. Most of you may have already seen it or will get it in the next few days. Never know how much truth is in these types of e-mails but would be interested to know by someone in the know... Here it is... I don't know what you guys are paying for petrol.... but here in Durban we are also paying higher, up to R7.35 per litre. But my line of work is in petroleum for about 31 years now, so here are some tricks to get more of your money's worth for every litre. Here at the Marian Hill Pipeline where I work in Durban , we deliver about 4 million litres in a 24-hour period thru the pipeline. One day is diesel the next day is jet fuel, and petrol, LRP and Unleaded. We have 34-storage tanks here with a total capacity of 16,800,000 litres. Only buy or fill up your car or bakkie 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 fuel, 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. In slow mode you should be pumping on low speed, 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 tank is HALF FULL. The reason for this is, the more fuel you have in your tank the less air occupying its empty space. petrol evaporates faster than you can imagine. Petroleum 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. Another reminder, if there is a fuel truck pumping into the storage tanks when you stop to buy, DO NOT fill up--most likely the petrol/diesel is being stirred up as the fuel is being delivered, and you might pick up some of the dirt that normally settles on the bottom. Hope this will help you get the most value for your money.

That's interesting Bluey.
The temperature to density thing is true, when we measure fuel coming out of fuel trucks on sites in Africa, the temp when filling the tanker at the refinery is always noted and there's some formula used to work out the change of volume to due temp changes in the tanker when it's dipped at the end of the day when it arrives on site.
hard to tell when you're just looking at a fucking stick with notch marks on it though !

Having said that, I wouldn't think a submerged fuel tank at a servo would vary in temp much at all by itself. How deep are they buried ? a couple of feet at least?maybe four? and under a concrete slab of about 6 inches at least if it's gunna take a fuel truck on top of it. So it's well insulated from the air temps above ground.
The temp change from the fuel going into it from the tanker compared to what the existing fuel temp is in the submerged tank at the servo probably has more effect on the overall temp. So a fresh tanker load would probably raise the temp and density which would mean you might have less fuel when it cools in your fuel tank.

It would also be interesesting to know what the maximum amount of evaporated fuel can be suspended in air to see how much fuel is actually lost when you replace that air with more fuel. Not much I reckon.

I got an email about those tips here in the states but never herd them explained.  Didnt know about the floating roofs in the tanks and that petrol evaporated that quick.

Interesting article.

Rocket is right about the temp variations in an underground tank.

Another point, while driving around with a full to half full tank might reduce petrol vapour, the author of this article overlooks the fact that petrol is heavy, and it uses more fuel to carry all that extra fuel around. In a 60 Litre petrol tank half when it's haldf full it weighs 21 Kg. Lugging an extra 21 Kg around perpetually woud use more petrol than would evaporate in most cars.

Excellent tips, like the one about the tanker delivery fuel, that makes a lot of sense.