Gas Cap Leakage/Evaporation

[John Simion]

My car has the 70 mm gas cap from 1967-1971 (the kind with three outer tabs and the big “VW” logo).  The old gasket had disintegrated to the point that essentially there was none visible, and I was losing a lot of gas by evaporation.  You can’t buy a new cap like this locally, and I tried ordering a new replacement from jBugs, a VW vendor.  It fit well on the tank but it was complicated with springs inside, and thus was too tall to fit under the hood.  As a temporary (?) fix, I bought a roll of material from O’Reilly that is supposed to be capable of sealing against gas, and I cut it to fit the inside of my old cap.  This stuff is pretty thin so I put two layers of it in the cap.  That has reduced the evaporation a lot, but my nose can still smell gas within a foot of the cap and it seems like I am still losing a little gas.  I don’t get it — I used to own a 1971 Ghia and I don’t remember smelling or losing gas out of it.

You can find “restored” 70 mm VW gas caps on eBay, but the sellers want a fortune for them and I can’t see any real difference between those caps and what I have, other than they have a cork seal.  I was able to find a 70 mm cork seal on eBay, so I ordered one and will try that.  Once I get the cork, I was also thinking about wiping a tiny bit of petroleum jelly on the cork to help it slide and seal better.

And another question I had was about venting.  I know venting must be done, but darned if I understand how this tank could be vented with this very simple cap and (hopefully) a tight seal.  Of course with my current incomplete seal, I have an unintentional vent, but assuming I solve that eventually, I’m a little concerned about next summer in Vegas!  I don’t want to solve one problem in order to create another.

I am wondering if anyone else has this same leakage/evaporation problem and if so, how did you address it?  Would it be worthwhile to just outright replace the tank and have the filler neck cut down even lower than my existing tank?  Assuming that can be done, it would at least let me use the jBugs gas cap.  But the jBugs cap also uses cork just like my leaking OEM VW cap, and I don’t really want to mess with it if I don’t have to.

johnsimion2015-11-24 14:37:32

[Author]

Posts