Every time I go to get gas and unscrew the gas cap on my 92 305 tbi camaro it makes a hissing sound like it is realeasing a lot of pressure in the gas tank. Is this normal for pressure to build up like that? If not, what could be causing this? Thanks

 

my 90 RS does that too. i was wondering the same thing. anyone with the answer to this help us out

 

i am pretty sure it is normal. in fact i believe your gas cap is supposed to hold pressure.....

not 100% tho...

 

Anyone else know for sure? I just wanna know is everyone elses does it too.

 

Yes, mine does it, as should everybody elses. I believe the gas fumes cause a build up of pressure in the tank. Anyways, that is why it is very important to depressurize your gas tank (per Haynes/Chilton's) any time you're working with the fuel system, especially when opening any of the lines, i.e. disconnecting the Fuel lines from the TBI. Otherwise the pressure in the tank will inturn force the gas out of the lines, and cause a dangerous mess.

 

But why does this only happen on my 92? My LS1 doesnt do that and either does any of my fathers vehicles. What causes the pressure to build up inside the tank?

 

Come on guys, please help me out here. Is this a problem or not? Any info would really be appreciated. Thank you

 

It's fine. It's normal. It won't hurt anything.

Gas (as with any other liquid) expands as it gets warmer. Doing this will increase pressure in the tank. There's another vent that will release some pressure if it gets too high, but it can't let all the pressure out or it would eventually cause all your gas to evaporate into the atmosphere polluting the air we breath. Plus it'd be a major PITA after work going out to a car with an empty gas tank every day.

A gas can will do the same thing (build pressure) if it sits in the sun. So don't leave it there or........

KABOOM!!!!!!!

 

That theory would seem to be true, but I could go out in 20 degree weather after the car had sat over night and unscew the gas cap and still hear the pressure releasing. I dunno, none of my other vehicles ive ever driven have done this. Do all TBI's do this? Thanks for the info. Does anyone elses car do the same thing? Does anyone elses car not do this?

 

Sometimes it hisses if there's LESS pressure in the tank than outside.

If you think about it, since gas (as with any other liquid) expands as it gets warmer, then wouldn't it makes sense that it would also contract when it's cooler?

I guess I can understand your concern if you've never noticed it before. The trick is to remove the gas cap quickly so you're not able to hear the hiss. Then it'll never bother you again.

Kinda like cranking the stereo so you don't hear the wind noise coming through the window seals, or if you don't feel like listening to your 3 1/2 yr old son's 20 THOUSAND questions.

 

mine has done it since i bought it and so does every other third gen owner that i know so i dont think its a problem ive never had one at least

 

the only time mine dosent do it is when im really low on gas......i guess you could be glad to know that you dont have any leaks in your fuel system

 

thats true, thanks guys for all the help

 

You might want to read the gas cap next time to fill up. For those that don't have the factory gas cap it says "Caution fuel spray can cause injury open slowly." Hope this answers your question.

Steve

 

It really doesnt matter if i open it really slow or really fast, it does it either way. I'm pretty sure it sounds normal though so i'm not worried anymore thanks to you guys.