The emptier my tank gets the more it does this and the warmer it gets the more it does this. It's a slight pressure build up of petrol funes in the tank as the liquid has room to evaporate. the emptier the tank the more space there is for the gases to evaporate into. A tank vent eliminates this as a general rule of thumb so can only imagine that they don't vent enough or are blocked. It hasn't stopped any of the cars functioning properly so has never bothered me.
-
UrS6 Stroker + HTA3586 =
-
Mine do that too but only in sring and summer when the temperature is hot , in the cold days doesn't do it.audi s2 aby red 1993 powreded by prjComment
-
+1 Mine has always done this. Perhaps there is a one way valve in the cap? The system has to let air into the tank, but there's definitely a build up in positive pressure when the fuel/air inside the tank expands.91 Modded 3B
14 A6 Avant Black EditionComment
-
Yep, I had a CQ that did this. In fairness the tank was rarely brimmed so I put it down to what JP said. On the odd long trip when I near on filled the tank, it went away or was a much smaller release of gas.Comment
-
i think its down to how often you re-fuel.i only ever stick 10-20 in at a time if going local so it goes down quick.never get the noise unless i have left it a few weeks etcComment
-
Mine does this and i cant get it full of fuel!
The fuel dispenser at the station cuts off because fuel starts to come out!
Just half tank full and i cant fill it more!!
Any ideas???Comment
-
I think there's enough of us getting that noise to assume that it's normal.
If you can only get 30 litres or so in your tank then it may be you've got another real problem that has caused your tank to collapse to half the size. I suggest you check the tank.
JohnComment
-
I agree that isn't normal, and nothing related to the gasses building up when the tank is getting low...Comment
-
The evap system is blocked somewhere or somehow. Check to see if the n80 valve is not blocked or damaged as this valve is meant to allow the excessive fuel fumes to come into the engine and get burnt thus not allowing them to get built into the tank. If for whatever trash the hoses are blocked then that's why you get the hissing sound from the tank and that's why you cannot get it to fill up to maxComment
-
Mines just started to do this after changing fuel line (and engine) to the point where I have to release the petrol cap really slowly to let pressure out or it chucks fuel back out the filler tube
Comment
-
a small amount of pressure is normal surely.
the only time i have ever seen a pressurized tank was on a pd engine vw. the injector seals were hardened allowing pressurized fuel to leech back. believe me there was some serious pressure when removing can.
i would think a little hiss of vapour is normal.Comment
-
It's definitely not small, much more than it used to do previously
Comment
-
Just found this thread, and in particular Error404's comment (from some years ago):
"mine has always done this, nothing has changed since i binned the EVAP line and now vent direct to atmosphere under the rear bumper
Dunno if the breather tank thing and rollover protection valve are jammed shut or somthing?"
I am just looking for some more info about removing the EVAP line, Error404, do you seal / bung at the end that leads to the cannister?
Also, how have you vented out to the rear bumper, and do you need a valve, or small filter?
Any info apreciated. I am in the process of replacing the fuel lines on an ABY coupe and looking at making the job easier by removing the EVAP line.
Comment
-
A blast from the past, my problem turned out to be the pipes getting put back on wrong after fitting new ones
Comment
Comment