Petrol tank sucktion.

Hi,,, does anyone know why when I open my Jimny's petrol cap does it suck in large amounts of air? Is this normal?

Cheers
Tony.

Good Q, I would like to know too, but keep forgetting to ask!
I cannot think how this can be normal?
Gaz

Someone here will know Gaz. I've not experienced this on other cars? I mean the sucktion (or do I mean the suction) ???? I thought perhaps it was because the tank or petrol line was leaking or evaporating, which could cause a vacuum within the tank, but I'm unsure and just guessing.
Tony.

Hi, Tony...long time, no speak, hope you're okay:)
I've had half a dozen Jimnys, and to be fair, they've all done this, without any issues...
....suppose it depends on what you mean by "large amounts"...
...when I open my cap, it literally a 'phtt', and it's gone, one second or less...
How does this compare with yours ???

This vacuum nonsense is part of emission regulations, old fashioned tanks are vented and allow fumes into the outside world. More modern (relatively) systems let the fuel pump retain a negative pressure in the tank. At rest any expansion in gasses are allowed to escape to EVAP charcoal cannister. In the event of an accident (roll over) there is far less chance of fuel escaping.
Chris

Now then Gus,, How's the rum bottle, still half full, yes??? regarding the issue, it used to be a 'phtt' less than a second, but now it's more like a sharp intake of breath, 'a higher sound volume,' but, only a second or so. Chris has explained why, it's negative pressure due to petrol fumes not being allowed to escape through vent holes, like they did in the old days, and to be honest in the last few weeks I've noticed a whiff of petrol around the car, strong enough to be detected but not enough petrol to hang around for more than a moment or two. I wondered if the two were related.