W124 Cabrio, fuel leak: filler cap

[geordielux]

Morning all,

I have searched the forums and still can't seem to find what might be the cause of a small leak that seems to come from the filler cap on my cabrio.

The petrol seems to be coming back past (or through) the filler cap. It is a non vented cap (correct mercedes part number) and there doesn't seem to be any leak from the neck of the tank or the breather pipe when I check behind the lining in the boot.

The leak seems to happen after a few miles of driving, even when the tank is not that full, so it seems not to be the over filing problem I have seen mentioned. The petrol is sitting around the filler cap and a few drips come out and down the rear wing. It even appeared that there was petrol around the tiny hole in the filler cap itself. There is no rush of pressure when I open the cap though.

Does anyone have any suggestions or is there any other breather or vent that I should check?

As always thanks in advance for any pointers you can give.

Michael

 

[kth286]

you have an overflow drain tube to take away any drips from the fill up nozzle, that could be blocked.

also there is a complex venting system that links to a charcoal filter inside the NSF wing .

The filter needs changing at 72,000 miles and never seems to get done, with the risk of a collapsed fuel tank in time - several instances on the various forums.

 

[geordielux]

Thanks KTH,

Think i have traced it to a faulty seal on the cap itself, a new cap seems to have fixed it and i get the slight hiss of pressure now when opening the cap.

M