JIMBO7

So my fuel system is 'pressurized' as it all releases when gas cap is removed.

So how does water get into the tank during a heavy rain if the drain in the tank fill rubber surround (boot) is plugged with leaves or whatever? I mean it's 'pressurized' right?

F22

Condensation is how water gets in the tank.

RollaMo-LT4

The "pressurized" part of the system is from the fuel pump to the injectors.
Not so much the fuel tank, although there can be some pressure build up.
But that is from the normal heating/cooling cycle of the surrounding atmosphere.

You can prove this, by taking the fuel cap off and noticing the engine will still run.
Although (at least on later models), it will cause the "Check Engine" light to come on if left off or loose for any length of time.

Sweet 90

Bad gas cap.

JIMBO7

So the cap lets water in even though it keeps the air pressure in?

inedajob

I think you hear suction when removing the gas cap, not pressure release.

Sweet 90

If you have a bad gas cap, it will not let any pressure build up, allowing water to enter, especially if your drain is plugged.