Why do most automobile owner's manuals warn the owner "do not top off the gas tank when filling up"?

Question

Why do most automobile owner's manuals warn the owner "do not top off the gas tank when filling up"?

Answer 1

Most fuel pumps in cars these days are in the tank. You need a little air in the tank or it will put to much pressure on the pump. Most gas station attendents suck ***, when you fill up your tank you are supposed to fill until the pump clicks off, after that most attendents will add more fuel to round you purchase to the nearest dollar (for paying convienence I guess), this is wrong. Once that pump clicks off do not add any more fuel. Pay the 23 cents

On the other level of your tank, you should never let it go below a quarter tank of fuel, again the fuel pump is most likely in the tank and belive it or not the fuel helps cool the fuel pump, when you go to empty the pump is no longer submirged in fuel and shortens the life span of you pump

Answer 2

In California, there is constant suction close to the tip of the dispenser, which helps keep fumes from escaping, so if you keep re-starting the thing every time it automatically shuts off, you are paying for maybe a quart of gas or more that's being sucked back into the underground tanks along with the fumes.

Answer 3

When the gas expands and contracts in your tank you have to have room to contain it. When it overflows it goes out onto the street and into the environment. It can be a fire hazard around the gas pumps as well. It's smart and responsible to stop after that first "click" on the nozzle.

Answer 4

Topping off the gas tank may lead to spillage.

Answer 5

Gasoline is around 55 degrees when you put it in your tank. On a hot day it will expand when it heats up and overflow the tank.