> What Octane gas does a 2.1L waterboxer need?
> I've been using 87 and my mechanic was questioning this.

it takes 91 octane (ron) ... but only in Europe!!!

the problem comes about in the way that the U.S. "measures" octane ...
they don't use the same method as the germans/europeans ... over here,
that same octane is numbered at 87 ...
due to the difference in formula/calculation.

now, the mechanic is gonna get all fluffed up and self-righteous and
tell you that you should be running 91 octane in the u.s. ... ain't
so. it runs fine on any octane (except 85, out in montana/wyoming). it
does, however, seem to notice the 10 percent ethanol stuff. :( so if
you're concerned, you might want to spend the extra cents to get 89
octane hereabouts.

here's what the 1988 vanagon owner's manual, straight from VW, says:
p. 74
<begin quote>

Vehicle Operation
Fuel Supply

Your vehicle is equipped with a catalytic converter and requires
unleaded fuel with a minimum octane rating of 91 RON  which
corresponds to an antiknock index (AKI) of 87.

Your vehicle has a smaller fuel tank opening, and gas station pumps
have smaller nozzles. This will prevent accidental pumping of leaded
fuel.
.....

Octane Rating

Octane rating indicates a gasoline's ability to resist detonation.
Therefore, buying the correct octane gas is important to prevent
engine "knock", which reduces performance and may cause engine damage.

Under high load operating conditions, unleaded premium gasoline MAY BE
USED. <emphasis mine>

The 91 RON octane rating which you will find above the filler neck is
based on the research method.
The AKI octane rating usually displayed on U.S. gasoline pumps is
calculated as follows:
Research octane number plus motor octane number, divided by 2.
< (RON+MON)/2 >

Regular fuels have an octane rating ranging from 91 to 95 RON
(Research Octane Number)
or 878 to 91 AKI.

Do not use any fuel with octane ratings lower than 91 RON or 87 AKI.

<and two more special interest paragraphs>

Gasolines containing alcohol

Gasoline containing alcohol is available at gas stations in some
areas.
<this is a 1988 vanagon manual>
The gas pump may not be labeled to identify that alcohol is present in
the gasoline. If it is labeled, it may
not identify what amount and type(s) of alcohol are used.
We recommend you use quality gasoline that is NOT <emphasis theirs>
blended with alcohol.
<as if we have a choice these days>
The use of fuel containing alcohol can cause loss of fuel economy and
driveability and performance
problems.  If these problems are experienced, we recommend you switch
to another brand of gasoline.

...

If wrong fuel was put into your tank

Premium gasoline instead of regular

Your engine runs equally well on premium gasoline, however neither
fuel consumption nor engine performance are likely to be affected.

<end quote>

hope it helps.  good luck!
unca joel