For the gas gauge in the vanagon to be accurate, it has to receive exactly
10 volts.  There is a little voltage regulator that is supposed to do that,
and the Bentley manual tells how to check if it is okay.  If you remember
reading about the near-murder in Springfield, Missouri, it had to do
with this very piece.

If you know what kind of gas mileage you're getting, you can use the
trip odometer quite handily.  Example:  20 mpg times 16 gal tank, you
should be able to go 320 miles before filling.  So fill up at 250, you'll
always be okay.  Just remember to form the habit of punching the trip
odometer when you fill.

Why wait till the gauge is way at the bottom anyway?

Will Self
Billings, Montana
'84 Vanagon