Mr Srinivas,a friend in Bangalore,e-mailed some dos and don'ts for car-owners when they drop by at a petrol bunk to fill up their tanks.
1) Do it the early morning when the ground temperature is still cold. Service stations have their storage tanks buried under ground. The colder the ground the more dense the petrol, and when it gets warmer petrol expands. Buying in the afternoon or evening....your litre is not exactly a litre.
2) Filling up, do not squeeze the nozzle trigger to 'high' mode. The trigger, if you haven't noticed, has three modes - low, middle, and high. Pumping in on 'low' mode minimizes the vapour that is generated while pumping petrol. All hoses at the pumping station have a vapour return. If you pump in on the high mode, some of the liquid that goes to your tank becomes vapour, which gets sucked back into the underground storage tank.
3) Fill up when your tank is HALF FULL.The more Petrol you have in your tank, the less is the air occupying the empty space.Petrol evaporates faster than you can imagine.Storage tanks have an internal floating roof, which serves as zero clearance between the Petrol and the atmosphere, so it minimizes evaporation.
4) Do not fill in petrol in your car, if you find, at the service station, a petrol truck pumping it into the storage tanks.Chances are that the petrol in the storage tank gets stirred during petrol delivery process. Filling up at this time, you might get in your car tank some dirt that normally settles at the bottom of the storage tank.