Hiss when the fuel filler cap is removed?

[Adrian Reeve]

Good afternoon all, I’m slowly working my way through the smallish list of minor niggles with my newly acquired 05 2.7. One of them is a pronounced hissing noise when I take out the fuel filler cap to add fuel. As this is my first Porsche I’m not sure what is normal, but in other cars I’ve had, this would indicate an issue with the filler vent, so a vacuum is being built up as fuel is used. Am I on the right track, and if so, where do I need to look please? Thanks very much

[Paul P]

Adrian. 

wirnessed this on your car first hand.
 

It’s not normal.  

I have some docs on the vent system somewhere will dig them out and send them on

 I thought the vent system was about “pressure, not vacuum” so maybe start with with fuel cap before getting deeper  

Cheap from OPC likely they will post.  (Ask for club discount - either tipec or pcgb from Tonbridge) 

[Adrian Reeve]

Thanks Paul

[Simon_R]

I thought most cars vented / hissed when undoing the fuel filler cap, especially when it’s hot like now? Most cars I’ve owned have to a degree? 
 

Or is this a different issue?

[Paul P]

Don’t think all cars do it, depends on the evap system. But yes a little hiss is not unusual 
 

When I heard it on Adrian’s car it was (to my ears) more like a suck than a blow and went on for a good few seconds rather that a short burst. 
 

it was unusual, in duration and how it tailed off towards the end.  

[BBB]

40 minutes ago, Paul P said:

...it was (to my ears) more like a suck than a blow and went on for a good few seconds rather that a short burst. 

 

it was unusual, in duration and how it tailed off towards the end.  

Cripes! Thought I was browsing incognito for a second.

[Menoporsche]

Private Browsing!

[Freeman]

Mine does the same. Will keep on watching.

[Cocky]

On 8/13/2022 at 1:09 PM, Paul P said:

Don’t think all cars do it, depends on the evap system. But yes a little hiss is not unusual 
 

When I heard it on Adrian’s car it was (to my ears) more like a suck than a blow and went on for a good few seconds rather that a short burst. 
 

it was unusual, in duration and how it tailed off towards the end.  

@JonStaI think I've figured out where our tailored ads come from 🤣

 

This is perfectly normal to anybody getting into a cold car or even fueling up with fresh petrol and warming it up by driving hard. The cooler the tank is to start with the more hiss you'll get when the cars hot. We don't have a simple hole in the filler cap like a motorbike. If you feel it it's extremely bad I would be checking the fuel vent/ breather valve the next time it's on a ramp or you're tinkering, even just replace it for your piece of mind. 

[sa utah]

All of my cars do this.  Including my 2.7 987.

[Adrian Reeve]

Thanks all