It's my understanding that the originals were "Vented" one direction
atmosphere into tank only, these caps will have a warning label on them as well to beware of pressure when removing. I believe all new caps vent both ways in and out with different pressure settings.
The vent's are spring loaded and should not allow fuel to pass as in turning corners or sloshing fuel. If it does the cap is bad.
I do know the later 70-71's 25 gal. tanks were vented through a charcoal filter in the rear roof post and didn't require a vented cap.
I have the newer style 2-way cap on my 68 and you can smell it outside of the truck in the summer sometimes, but it never spills fuel.

Mark D.

1968 W200 Sweptline
1969 D100 Utiline
1971 D100 SE Sweptline
1993 D250 Club Cab Sweptline
1986 W250 Cab & Chassis
1978 D300 Sweptline

E. Brookfield, Massachusetts



Edited 1 time(s). Last edit at 12/26/2017 09:24PM by swptln.