General Petrol tank vent

[chase]

Hi All,
Son borrowed my posh car leaving me with his '97 Mk 1 punto , naturally it needed fuel , when removing the fuel cap( after driving 10 miles to work ) there was a sucking in of air so presumably the tank vent is blocked .
Question , how is the tank vented ? and how easy to fix ?

 

[s and b]

its designed like this

 

[chase]

So its normal to have the tank pressurised ?

 

[fingers99]

Or unpressurised! Lots of potential reasons for it, but if the car runs OK, I'd leave well alone.

 

[chase]

Actually it sounds like its under a vacuum , e.g. fuel being drawn out the tank and not being repaced by air at atmospheric pressure .

 

[thelad]

Actually it sounds like its under a vacuum , e.g. fuel being drawn out the tank and not being repaced by air at atmospheric pressure .

lol, has it sucked the tank in?

 

[AndyRKett]

This is quite normal the idea being as fuel vaporises in the tank you don't suck in clean air creating the perfect combustible mix

Also a breather pipe also has the potential to let fuel vapour escape into the atmosphere which is against eu emissions rules and regs

Normally the fuel vapour would fill the space but it's still sometimes leaves a bit of a vacuum