when opening gas cap

[zacatecas]

Why is it when i open my gas cap air comes out and there times that it doesnt?

[dj_ender]

In my experience, the rush of air only happens on an empty tank.

[ExplodingCake]

Gas tank gets pressurized during operation.

[illinois_erik]

Why is it when i open my gas cap air comes out and there times that it doesnt?

well your fuel system is pressurized, the tank will hold a bit of pressure. Pressurized gasoline vapors more specifically.

Having it moreso when the tanks almost empty is just because theres more vapor in there, the gas sloshing around hastens its evaporation.

When it doesnt happen..cant say exactly why, anytime I crack my gas cap I get pressure release, just a lot more when Im "running on fumes"

its normal jsyk

[Fleetw00d]

Warm tank during the day may cool enough on a cold night to significantly reduce the pressure retained in the tank.