exactly what that overly strong spring will cause.
Since they are making them so nothing can escape, they made a monster.
If the spring was very weak (1/10 psi check valve)a full tank in a cold condition would suck in air as the gas contracted. Then in the full sun the gas would expand and create a lot of pressure (probably has a warning sticker that says be careful of pressure when opening)so the strong spring doesn't let the air in until a substantial vacuum is created. The whole design is dumb.
Original vented caps had a tiny vent hole so the tank could breathe without any effort.
