Sigh, not this crap again.... BS. Petrol tanks are buried underground precisely for the reason of keeping their temperature constant. Ground temperaure will vary by only a few degrees over the course of an entire YEAR, let alone day/night or winter/summer (this is the entire principle behind ground source heat pumps for year-round reverse cycle air-con - the ground is warmer than the air in winter and colder than the air in summer). And the difference between the specific gravity of petrol at 10 degrees C (an approximate ground temperature) compared to 25 degrees C (air temperature) is in the order of 1-2% - ie over for a 100L tank you might get 1-2L less. Remember the density of liquids is MUCH less sensitive to temperature compared to gasses. Also, I've read that most pumps these days compensate for changes in density - ie they dispense mass flow, not volume. And I have yet to come across a bowser with "high, medium and low" triggers. If I just squeeze the trigger slightly it will trickle in, any more than that and it is basically constant flow (the speed is determined more by the shape of your tank and filler neck - for instance on the same bowser pump the AE102 fills much faster than the JZZ30 because the Corolla tank is under the back-seat whereas the Soarer tank is behind the seats in front of the boot. As for the fuel churning into vapours and getting sucked back out, once again you are only talking about a fraction of a percent in the short period of time that you are filling the tank. If you stand there and let the fuel trickle in you mightn't be churning the fuel up as much, but at the same time you are spending much longer filling the tank and thus allowing the fuel IN the tank more time to flash to vapour and get sucked out. Doesn't matter, since properly functioning car petrol systems are one-way sealed. The petrol cap can let air in to accomodate for consumed petrol, but cannot let vapour out. If excessive vapour builds up in the tank then it is syphoned off and condensed in the charcoal canister and then burnt under vacuum. It does not escape back out to the atmosphere as this is an emissions violation and has been this way for probably 30 years. Improperly operating fuel caps or charcoal canisters (ie ones that aren't serviced properly) can however affect this. So you're telling me that they don't have filters on the bowsers? Even if they didn't, you still have a fuel filter or two in your car, so even if you did suck up a little sediment you're not going to grenade or engine (and it'd have to be a fair bit of sediment to clog up the fuel filter to. Or are you saying that the volume of sediment will mean you get less petrol :P In short, you will save significantly more money by just filling up when the price is cheapest and driving more conservatively than ANY of these so-called "tips".