Should gas cap always hiss when removing it?

For the last year I was getting a couple of evap codes. I was just clearing these codes then they would come back and then the cycle would repeat itself. I knew what the problem was I just didn't want to take the time or spend the money and fix it. I was getting a pretty strong gas smell from my driver side rear tire. I figured my tank was bad or I had a bad gasket on top of my tank.

I took my truck in and to find out I had some very small holes on top of my tank. I got my truck back today and everything was replaced except for the fuel pump!!! New gas tank, check valve, check valve gasket, new filler tube, and other gaskets on top of the tank.

My question is does the gas cap always hiss when you remove it. Is this normal operation? Now after all of that work is done on my truck my gas cap does NOT hiss when I remove it after driving. Am I missing something or not? This hasn't operated properly in about a year so I forgot how it should operate normally.

Sorry so long.

 

Sometimes mine hisses, other times it does not.

 

Someone told me it's not supposed to hiss. Mine usually does though.

 

What codes were you getting? Do you remember?

 

not if its been sitting overnight but if the truck has been running such as stopping to get gas then it should have a "release" when you open the cap.

the extent to how loud it is changes with the weather conditions but the pollution system sucks a vacuum on the tank so no fumes escape to kill the polar bears or some stupid shit but yes its normal to hear a little pressure equalization when removing the cap if everything is sealed properly and you have no holes or bad gaskets anywhere in the fuel tank

 

I was getting P0440 and P0446. I also put in a new charcoal canister last fall.

 

Most times the noise level at the Quicky Mart is so high I would have to have my ear very close to the cap to hear anything

 

Gas cap hissing is normal to an extent. This is especially true if you run your tank low on E often. As previously stated, the fumes in the tank expand and contract within depending on weather changes so the volume of the hiss will change based on what time of the year it is.

Now, a system that has a faulty evap system will cause more hissing than not more often than not, simply because it is not taking the excessive fumes and purging or venting it out of the system like it is supposed to when needed. So excess pressure (lack of pressure if you have a leak) will exist within the tank necessarily due to defective components.