When my 87GL with auto trans. & AC is working, I'm averaging 20mpg.  I
usually fill up around every 250 miles and get somewhere in the
neighborhood of 12 gallons.  Most of my driving is highway though.  When
she's sick, of course, I don't get that good of mileage.  But around
20mpg has been pretty steady since I got it.

Tonya
87 Vanagon GL
74 S. Beetle