>There's a sticker beside my fuel cap than says minimum octane to put into
>the tank is 91.

I think its time for the annual lesson on octane.

Back in the dark ages (prior to the US government confusing the issue) there were two ways of measuring fuel octane, motor (based on observing the fuel's performance in an engine), and research (based on chemical analysis).  These methods gave different numbers, with research octane giving the higher number.  The US government couldn't decide which one to use, so they invented a third system! (the average of the motor and research numbers)

So, if a gas pump in the US says 87 octane, its really 91 research octane, the minimum for our Vanagons.

Take a look at the sticker on the (US) gas pump next time you fill up. The fine print will say (R+M)/2 method, or something like that.

Bill