Originally Posted by JimN
They need to specify whether it's positive or negative pressure. Either can mean the vent line is clogged.
It would be nice to know that, I agree. But it's pretty hard to determine that from just a sound coming from the fuel cap. It isn't like a gush of air you can feel with your hand. It appears like my system doesn't have a provision to let air out of the tank, like if things heat up and expand.. But I refuse to believe there isn't a provision to let air into the tank to replace spent fuel...