E90 320i N46 Expansion bottle

[eamo]

Tell me this lads should one be able to remove the cap off the expansion bottle when car is idling after it has been driven for a 20 minutes?
Obviously you'd have to screw it off slowly to release the pressure but in doing so if it starts gurgling out water whilst doing so I assume there's to much pressure and could be a symptom of head gasket failure?

[Valdelisbmw]

u can't open after 20 minutes of drive, its under full pressure .u must wait ,let it cool down , and only after ,can open it ,and slowly .not common for head gaskets .once its not overheating to should be all ok