Should air hiss from gas tank when opened?

[TechnoLoGs]

It does this when its running OR off. Is this normal operation, or is it a problem?

Symptom: Car runs, car gets turned off, you go to gas station, MUCH air hisses out of the cap when its opened.

The gas guy thought the tank was near empty, it took 10 gallons. Fuel gauge was at a quarter, or so.

Is this a problem, or is this what gas tanks do? (It also does this when it is off.)

*This is an ANY CAR question, not only specific to my Taurus. Cap and everything looks original.

Thinking of getting Gumout, but my tank is full now, so nit sure how well it would work.

 

[GreeCguy]

Normal.

 

[ARCOgraphite]

Normal.
If you have a EVAP issue on a OBDII you will get a MIL lit.

 

[SLCraig]

I think it's actually air going into the tank, when it happens on my car, and it's normal on the vehicles I've owned.

 

[Schmoe]

Yes. All new cars have an EVAP setup. In so much, that EPA no longer gives a gas station emission credits for having secondary vapor recovery nozzles....

 

[147_Grain]

Normal. Fuel / gas vapors heat-up and expand in the tank, thus pressurizing it a bit.

 

[Michael_P]

I remember back in the 1980's, I poked a hole on a large can of butane and poured the contents of it in my Onmi GLH fuel tank expecting it to go faster. I had so much pressure in that tank, that by the time I pulled over, the tank bulged so badly that one of the straps broke. The tank was half full. I drove home with the cap off, ran the tank dry, replaced the tank and evap canister and some lines for safe measure and all was well. I was 19 at the time.

 

[zzyzzx]

It means that your EVAP system is actually working. In fact if you never hear the hiss you probably should be getting a check engine light.

 

[SwampSurvivor]

I read

"Should hairy [butt] ..."

 

[chevys10]

My mazda used to get the hiss but doesn't anymore...I have a P0455 large evap leak code right now I am trying to diagnose..so yeah it is normal.

 

[Voltmaster]

Yes