80-84.5 (somewhere in 84) had a metal fill neck that was bigger and the tanks
had bigger holes in them to allow for this.  Then in 84.5 they went to the
smaller, plastic fill neck on the gas vans (all diesels had the metal fill
neck).  I think that they actually used some large hole gas tanks with the
small filler neck (you know VW: waste not, want not) because there is a seal
that is setup to use the small fill neck on the big hole.  All 85 to 91 vans
I have seen use the small fill neck and small hole in the tank.  I have taken
apart too many vans to think about.  This only applies to 2wd vans.  Syncro
vans have a totally different gas tank and fill neck system that I am
unfamiliar with (haven't parted or worked on any syncro gas tanks yet).

Just FYI,
Ken Wilford
http://www.vanagain.com
John 3:16

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