built up air pressure in '94 S320 gas tank

[WANT '71 280SEL]

I recently acquired a '94 S320. Whenever I remove the gas cap there seems to be significant air pressure, which I can tell because of the loud noise it makes when the cap is loosened. Is this normal? Is there some sort of vent that might be clogged?

Thanks
David

[WANT '71 280SEL]

I understand that pressure is normal, but from a search it seems that it's actually a vacuum and is perfectly normal. [Kept for the archives].

Thanks
David

[Hatterasguy]

All cars do that when they sit. Temperature changes cause pressure to build up.

Ever change the fuel filters on your old SDL on a really hot day after the car has been sitting in the sun? Fuel freaken pours out like Niagra falls, well until you pop the cap and release the pressure, duh.

[tvpierce]

I've had fuel spray out at me before, so I now make a habit of pressing on the cap while turning it, then holding it until the sound of the air escaping stops. This allows the pressure to slowly release.