Pressurised Fuel Tank

[Pete E55 Daly]

When I remove the petrol cap on my 1998 AMG E55 there is a whoosh of air as if the tank is pressurised. This is particularly apparent when the tank is not completely empty. I am getting reasonable MPG. Is there a vent blocked somewhere?

 

[Stevie A]

It's a pressurised system so you get the woosh. Don't worry about that at all, worry if you don't get a woosh