That's an interesting point.  The heater circuit is a complete loop so
the main pressure in the system should be able to reach the sensor from
one side or the other even if the valve is closed.  Since the water pump
is always exerting some pressure trying to move water thru the heater, I
suspect that the reading will either rise or fall when engine rpms
increase, depending on which heater hose is used.  This same effect may
also be possible to some extent anywhere in the cooling system.
  As with other vanagon gauges the idea is to become familiar with the
usual behavior so as to recognize the unusual.

Larry A.

mark drillock wrote:
>
> If you put the coolant pressure sender on a heater hose won't the gauge
> reading vary depending on whether the heater valve(s) is open?
>
> Mark
>
> Larry Alofs wrote:
> >
> > TinkerMan wrote:
> >
> > > 4. If anyone has a another good suggestion about
> > > easily tapping a pressure sender/switch into the
> > > coolant system (e.g. to the coolant expansion tank or
> > > vicinity), without drilling or such, I'd be glad to
> > > hear (better yet, seeing is better. Any pictures?...)
> > >
> > > =====
> > > Cheers, T-man.
> > >
> >
> > My tentative plan is to install one of the "prestone" type flush tees in
> > a heater hose above the spare, then use a brass female garden hose end
> > to adapt the pressure sensor or gauge tube connection and install it on
> > the tee in place of the cap.
> >   I'd like to keep the bleeder available for its original purpose.
> >
> > Larry A.