I had the exact same symptom. It turned out that I had a bad connection
between the long connector on the side of the instrument cluster to the foil
circuit. Repositioning the pins in the connector cleared it up.

Jim

On Sun, Jun 19, 2011 at 11:31 PM, Jeff Palmer <jpalmer@mymts.net> wrote:

> My temp gauge is acting up, I think.  85 Westfalia (automatic), 2.1l Boston
> Bob rebuild with about 20k on it.
>
> Coolant levels seem fine in both tanks (although by fine I mean that I seem
> to have to add coolant to the new motor, same as i did with the old, for no
> apparent reason ...)
>
> Today I'm driving about five km to the store.  The gauge is fine, then
> shoots up, then comes back down, then up again.  Then the light starts
> flashing, then stops.  Then the gauge goes back down to normal.  I'd been
> driving for a matter of blocks when it first pegged.
>
> Normal is slightly below where the light is located.  Used to be right at
> the light with the old motor, but at some point (not sure exactly when) the
> gauge started reading a little lower, and the gas tank did as well.  Maybe
> the voltage regulator.  Sorry for the red herring.
>
> Any thoughts?  Goofy gauge or something more sinister?
>
> Thanks as always
> Jeff
>