Chimp, pressure in Petrol tank !?!?!?

[Ston]

Hi guys,
Just got back from filling the Chimp up with petrol. When I came to undo the petrol cap, there was a big hissing sound as the tank sucked in a load of air, and I can hear the tank poping and expanding back to its normal size.
This has never happened before, so I guess its bad?
I am a bit dence when it comes to cars, all I know is I love my TVR, so I guess petrol is delivered to the engine by a pump (hence the fuel pump) as opposed to pressure? If so where is the valve for the petrol tank, this might have become stuck close, or did I just do the cap up too tight?

Hope one of you nice people can help.

Thanks in advance.

[manek]

Mine does that and always has. It doesn't seem to have caused any harm.

-Manek-

[icb]

Same happens to mine. When standing still usually makes noise, moreso when tank less than full.Dealers said is aluminium tank and is sometimes under a vacuum and other times is pressurised, and nothing to worry about. Steve Heath in his book explains purge system for tank, and seems difficult job to get at carbon filter in driver's wing. So I wouldn't worry about it, I don't!!Was bit worrying until explained to me.

[Ston]

Thanks guys.

[squirrelz]

Well my rover does that as well, so it must be fairly normal.

[Bob the Planner]

Mine did that for a while - getting at the filter is not that difficult. I did mine after it was too late - the tank expanded and the baffles that stop the fuel sloshing about have come away . Every time a go round a corner the fuel gauge cannot decide whether there is a quarter, half or full tank - its usually the former

Bob the Planner

[KarenH]

Agree with Bob the Planner. See "PRESSURISING FUEL TANK ?" thread around October 2001. Don't ignore the "big bang" hoping it will go away.