Gas Tank Pressure..Question
 

Hey guys,

I was fulling up with some 101 unleaded the other day at my tuners place...And a guy that worked there took off my gas cap and realized I had alot of pressure..(I always have a ton of pressure everytime I take off my gas cap)

He recommended that I get a new gas cap so my system can vent, What do you guys think? Are you guys getting alot of pressure when you open your gas cap? Should I really invest in a new gas cap? P.S. my car is basically stock intake, clutch, and fuel filter was just replaced if that makes any difference..

These questions are pretty noobish, I tried to do some searching under "gas tank pressure" and a few others, but got nothing....Thanks guys :101384_l:

Some pressure is normal. There is a pressure relief valve in the cap, but most of the pressure is normaly handled by the vapor recovery system. Are you having any other symptoms / smells. Replacing the cap maybe a good idea if your worryed about it.

No other symptoms at the moment really...I had some symptoms at one time, but it was all mostly vac lines and what not...

Just curious if the pressure was normal or not..:)

The pressure and the volume of vapor released depend on a couple of things:

1. How full the tank is - the lower the fuel level, the more vapor will form due to the empty space, and the lower volume of fuel warming up more from the exhaust pipe near it will create more pressure.

2. Gas with ethanol will develop more vapor pressure than gas without.

3. Winter gas will develop more pressure since it is blended to vaporize more easily in cold temperatures.

4. The gas cap venting pressure determines the maximum pressure allowed in the tank.

Most of the venting occurs thru the checkvalves on the tank. Look thru the manual and you should see the valves and perhaps even the setpressure, they vent thru the charcoal can for outbreathing but I cannot recall where they inhale from during inbreathing. Pressure in the tank is regulated in inches of water or something small like that but if that amount of pressure or vacuum is in the tank when you release the cap it will be audible, this is normal. Now if it blows your hand off there is a problem with the checkvalves as these things do not last forever.

What you describe is normal. No need to replace the cap. Keep the one you have.

One time I started smelling gas fumes. It turns out I had twisted the cap on too hard and it wasn't hold the expansion pressure. Bought a new cap, problem cured. The smell of fumes went away. So, I say keep your cap. It appears to be working.

what if there is NEVER ANY pressure when you take the cap off? Is this a problem? Also after filling the tank completely and taking fast right hand turns a friend following me said i was spilling gas on the road.

What's my problem?

Do you smell gas in the car?

Strange thing happened..

since I've got the car I've had that hissing issue after I open the gas cap .

Last weekend the car did something strange . it wouldn't start so i'd just had some fuel pump issues replaced the fuel pump so and so and I thought maybe I'd messed something up so
as Istart to take apart the fuel pump assembly , i hear a hissing from the tank as I'm taking screws off ..

I start to think , I take off the gas cap it hisses quite a bit . then i try to start the car

and it started up perfectly . it hasnt happened since , But I'm thinking that maybe its not that hte tank has excess pressure , But that its not breathing not replacing the fuel that hte engine is using with air ..

what could be causing this ? am I crazy?