Air Escaping gas tank when I fill up

[blackcat1134]

Hi all,
I've got an odd situation, apparently, every that I go to fill up with gas, I hear a small hissing sound when I insert the nozzle into the gas tank. It happens in cold and in warm weather, I'm just worried that it'll effect the MPG or some other problem with the car itself.

Any ideas on what this is? Thanks!

[Dan in NZ]

When the gas goes into the tank, the air gets displaced and comes out through the filler hole. Y'know, like when you jump in the bath and the water comes out...

[632 Regal]

lmao@dan

[blackcat1134]

I understand that, but it's just started to happen about 20,000 miles ago. Is this normal on a car that's over 100,000 miles?

[shogun]

Is it actually hissing when you open the fuel tank lid?
If so, then check your fuel tank airation system.
I know that the E38 had big problems with this and the vacuum became so big inside the tank, that the fuel tanks cracked.
Many had to exchange the tanks and had to install a modified airation system.
Sometimes this also can effect a bad warm start after a llonger drive. For example when you start with a full tank, then fuel level gets lower and vacuum increases and when you then try to restart the engine, the engine has to revv a long time still it runs.