This i got from Malaysia-today who got it from nst:

On a more serious note, the Federation of Malaysian Consumers Associations president Datuk N. Marimuthu gave some tips on getting more out of every litre of petrol.

“Only fill up your vehicle in the early morning when the ground temperature is cold. Remember, service stations have buried storage tanks.

“The colder the ground, the more dense the fuel. When it gets warmer, petrol expands. Thus, buying in the afternoon will give you a litre which is not exactly a litre,” he said.

“A one-degree temperature rise is a big deal for business. But service stations do not have temperature compensation at the pumps,” said Marimuthu.

He advised motorists to squeeze the nozzle’s trigger at a low speed, thereby minimising vapours created while pumping.

“Fast pumping will cause liquid petrol to vaporise and get sucked back through the hose’s vapour return mechanism. You are getting less for your money.”

Another tip was to refuel when your tank is half full.

“The more fuel in your tank means 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 minimises the evaporation.”

Marimuthu called on motorists not to refuel when a fuel truck is pumping into the underground storage tank as it could stir up sediment.