At 01:20 AM 3/11/2011, DW wrote...
>I have looked for a good reason not to run premium gasoline, but I
>can't
>seem to find any detailed information. I have always gone by the
>sticker on
>my van that states something about a minimum octane rating of 91.

If I'm not mistaken, the sticker refers to 91 RON (Research Octane
Number). That's the common octane rating in Europe. In the US, pumps
are marked with an octane number called the AKI (AntiKnock Index),
which is the average of RON with yet another octane rating, the MON
(Motor Octane Index), which is a much lower number for the same gas.
Many pumps show the rating method, saying something like "Minimum
Octane Rating (R+M)/2 Method." - that's AKI.

The short story - 87 octane regular gas in the US is suitable for your
91 RON Vanagon. There's no need to buy premium gas.