Petrol leak

[rwaw]

Filled up with petrol to absolutely full then drove home for about 20 miles; few days later drove car out of garage (about 5 yards/20 secs) and switched engine off to work on speaker; next thing I know petrol is leaking through lock on petrol cap.
When I took the cap off a few litres gushed out !
Car was on the level but in full afternoon sunshine; any ideas ??

280SL 1969 Euro RHD

[Richard Madison]

This might be related to the petrol cap being vented or not. Here's a discussion about caps.
http://index.php?topic=1310

If you use the Search button to find more on this topic, suggest you look for "gas cap" or "gas leak" since we don't use "petrol" on this side of the pond.

Richard M
 
 

[George Davis]

rwaw,

You noted that the tank was completely filled and then driven only 20 miles.  I think the likely cause was expansion of the gasoline.  Gas expands as it warms up, so if it was cooler on the day you filled it and warmer on the day it gushed out, that probably explains it.  Same thing happened a time or two in my Sprite until I learned not to fill it so full.

Modern cars usually have a built-in expansion space in the tank to prevent this sort of thing, but these old buggers don't.  It's best not to fill it absolutely full.  I guess the good news is that your tank handled the pressure well!

George Davis
'69 280 SL Euro manual

[Cees Klumper]

I always fill the tank to full capacity and (since I fitted the correct gas cap) have never had any sort of leak or pressure build-up as you describe. You may want to check whether the (small or, on US models, sometimes large) expansion tank that's fitted inside the trunk is operating properly (that is, whether the fuel line going to and from it are unobstructed etc.) and of course whether your gas cap is the right type.

Cees Klumper in Amsterdam
'69 white 280 SL automatic