Vacuum Hiss when fuel cap removed!

[PINBALL]

Anyone else get this?

Have had the same thing happen on previous E class Mercs.

Could the reason be something to do with a lesser chance of air bubbles getting into fuel lines & smoother, more constant performance?

Have never experienced it with other cars that have ventilation holes in thier caps.

Do the diesel cars do the same thing?

Regards, Keith.

 

[slk280rc]

This is normal. Its not related to smoother performance, etc, its to do with a different approach to the design of the fuel system. I think that environmental reasons now mean that fuel can't vent to atmosphere. Its not a complete vacuum (that would collapse the tank), its only a slight vacuum.

I don't know whether this also occurs on modern diesels. Hopefully someone will be able to tell us, who owns both kinds of car.

 

[robbi-wan]

My previous car was petrol and always hissed (when a full tank was ran to the bottom), and the C220 CDI does the same thing - so i guess it is normal!

 

[Stevie A]

It's for the fuel pressure is it not? It's normal no need to worry.

 

[television]

All fuel tanks run with a vacuam to limit the vapors that can enter the atmosphere, some are done with charcoal filters that store the vapor and drawn of by the purgeing switchover valve at coolant tempertures over 80 and combusted in the engine, but not when deceleration This is all sorted out by the control unit that uses,engine speed,air mass,temperture and intake air temp. Hope this helps

Malcolm

 

[PINBALL]

Thanks to all input.

Thats very helpful,
Cheers,
Keith.