Is it normal for a car's fuel tank cap to release gas when opened?

[TheoDella]

It is normal for a car's fuel tank cap to release gas when opened. Here is the relevant explanation: Pressure release: Gasoline is a highly volatile liquid. In hot summer conditions, the fuel tank is normally sealed off from the external environment to prevent fuel vapor from escaping. The fuel pump inside the tank also generates heat during operation. Both gas and liquid expand when heated, with gas having a much higher expansion rate than liquid. However, the entire fuel tank is a sealed space. As a result, the gaseous gasoline sealed inside the tank creates pressure that exceeds the external atmospheric pressure. When the fuel tank cap is opened, the pressurized gaseous gasoline is released. Carbon canister blockage: During summer, the fuel inside the tank is more prone to an imbalance between internal and external pressure. The rapidly rising temperatures may cause the carbon canister to temporarily fail to handle this pressure imbalance promptly, which can lead to the hissing sound when opening the fuel tank cap.