A Class fuel tank 'thunmp' MkII

[maldon]

The wife's A Class is making a strange 'thump' a few seconds after she parks, switches off and locks the car.

We've had the car along to Mainlymercs in Colchester (as usual, brilliant service) - they are sure it is from the fuel tank expanding, after it has contracted a little.

The fuel filter has been changed - but the problem still exists - the MM lads think it may be a problem with a blocked charcoal filter/vent.

Anyone have any experience, ideas or pointers?

Thanks.

 

[mattkh]

Hi
How loud is the thump and where does it come from ?
As for the tank, they are plastic these days.

 

[maldon]

Thanks, Mattkh - the thump is noticeable, a low sort of soft 'thump' the MainlyMercs lads reckon it is definitley coming from the tank - I was wondering if the tank is steel or plastic. I reckon that the noise, now thinking about it, is consistent with the tank being of plastic construction.

At least that part of the problem is now known.

Of course, Mrs has been trawling the internet and is now 'advising' me the tank is at anytime liable to rupture, spark and blow up.....

 

[Ellsy Tanners]

Hi,
The A-class fuel tanks are metal, however they are covered by plastic under shields

 

[wireman]

Perhaps the tank is becoming partialy evacuated by the emission control system and once stopped an air leak is allowing the tank to draw in air, then the tank pops back into its unstressed condition. There may be a leaky non return valve in the vacuum system associated with fuel tank emisson control. Many cars hiss slightly as the fuel filler cap is removed.