Fuel tank woes

[frankerooney]

Hi.
  I've got a problem with my (cough) vw scirocco. I KNOW it's called golf gti.com, but I've got a gti aswell.
Anyway, the problem is the fuel tank keeps pressurising - the longer the journey the more pressure you get. I've changed the gravity valve and checked the breather pipe isn't blocked. It's a problem because after a long trip yesterday, it was so pressurised in there that it was forcing petrol past the seams in the petrol tank - leaking straight onto the exhaust  :-[
Can anybody suggest anything? I'm at my wits end!

[mk1]

Hi. frankerooney.
Are you sure the fuel leaking is due to the pressure. The tank may be corroded on the seam (common). Not unusual to have some pressure in the tank when you take the cap off.
Steve.

[modulater]

Its rare to get pressure in the tank.

normally when the breather gets blocked you get a vacuum that will either make the car stall or as i saw on an astra actually suck the tank in and deform it.

You've checked all the pipes and the breather and say they are fine so I would also say its a leak of the tank or surrounding pipe work.

Next time you drive the car stop and remove the cap and listen and feel for pressure being released.

[frankerooney]

Cheers for the replies. Yes, it was pressurising the tank during driving, and slightly when the car was "just sitting there" with the engine off - I suppose that temperature changes vapourise the fuel and cause some pressure.
I did a 30 mile trip and there was masses of pressure in the tank - it took a couple of seconds with the filler cap off for the hiss to disappear, hence it forcing fuel out of the tank. With no pressure it hasn't leaked since.
I couldn't for the life of me work out where the tank released the pressure - there must be some way of equalising it - so I went down the scrappie and got myself a new gravity valve off a carb model - this lets the tank suck air in and blow out whereas the old one only let air in. So we're sorted now - no pressure in the tank and the car still runs fine. Just leaves the question of how the FI models are supposed to get rid of extra pressure with the one way gravity valve fitted???