Gas cap
 

When I take my gas cap off for a fillup there is no hissing sound. Does anyone elses ride do this? Most cars you hear the release when you take the cap off. Just noticed it so I don't know if it's something new.

Mine usually only does the hiss if I'm really low on gas.

I never noticed mine hissing until I moved to Utah. Could altitude have something to do with it?

I thought it was only sposed to hiss if your charcoal canister wasn't properly venting the gasses?

I read that there is a valve between the gas tank and charcoal cannister that opens when the pressure gets so high. So at a certain pressure, the vapors will go to the cannister and await a PCV event that is suitable for vapor disposal. Pressures below that certain level, would be maintained in the gas tank, unless you remove your gas cap and get hissed at. Maybe your cap leaks?

Iono if my car does it or not, it's illegal to self-serve in NJ. I do know that it passed inspection though, so unless it's developed a leak since then I doubt it does.

They don't pressure test the cap here. I'll probably just replace it. There under 15 buck.

Here's an interesting program in Ohio. They found the highest failure rate(though small) on caps on vechiles made between 95-99.
https://www.tmacog.org/CommuterServic...p%20Report.pdf

Someone (me) needs to get their act together and add stuff like that to the FAQ.

My new Yaris doesn't hiss, and niether did my '91 S-10, but my wifes '87 Civic hisses loud.

Replaced the old cap with a new Slant cap($6.99). Still no Hisssssssss.:confused: "shrug"

It's a function of your gas tank emmissions system - on the Toyota Scion etc they have a pump that takes the pressure out of the tank from 2-5 hours after you shut the engine off. Pressure in the tank only occurs if the gasoline evaporates faster than the engine can suck it into the engine while you are driving. Altitude will definately affect the pressure in the tank as will temperature changes. I would say that if you took a quick ride on a bumpy road you would have pressure in the tank but if you down shift a lot then the engine vacuum may remove the pressure via the charcoal canister.