If i fill my tank full of gas and drive for like half a tank or so, and then take the gas cap off, you can ALOT of air rushing in. This happens more when the fuel is low, im guessing because there is more air than fuel. Then the fuel gauge usually goes up a noticeable amount. My car also smells like gas sometimes. Its not really strong, like its leaking, but just slight. Does air need to get in the gas tank? My friend described it as if you are drinking water from a plastic bottle, and you seal your lips around it, when you are drinking it, the bottle collapses/crushes, and when you stop, and let air in, it takes shape again. This isnt happening to my gas tank, is it? I was also reading about how the PCV canister, takes away the gas smell, and creates vacuum pressure in your gas tank...could the PCV just be clogged or something? or do i just need a new gas cap?

Thanks for your help.