Vacuum in my fuel tank...

[ComCool]

I have a '99 civic VTI, and when I turn my fuel tank cover to put on fuel I can hear it sucks in allot of air, like there’s a really big vacuum. Is that normal? If not, do anyone have a diagram that describes the fuel system setup.

 

[codyj86]

actually i think its a pressure build up.... i have taht too

 

[Beelzebubba]

Your fuel tank and system is sealed to prevent evaporative emissions. Fuel will evaporate releasing hydrocarbons into the atmosphere causing pollution. You are likely hearing the pressure from the gasoline expanding due to heat escaping when you break the seal.

 

[ComCool]

I sound like is sucks air in, not out, but i will chech that out. I just haven’t head any other cars doing this, not at much anyway. I checked the valve under the car that equalises the pressure in the tank, and it seems to work when I blow air into it. But it cold be a hoses that clogged. But I needed a manual that shows how the whole fuel system I set up.

But if its normal on a civic then I’m not worried, it would just have sucked if the tank would have gotten damaged because of the pressure, and the fuel pump would have been damaged, because it struggles to take in fuel.