Both front and rear heater cores are on their own coolant circuit.
It's fed off the plastic coolant manifold on the right side of the
engine compartment, and returns to the nipple branching off the metal
coolant bypass pipe on the left side of the engine. Water runs through
the heating system regardless of thermostat status. Benny's site has a
nice little diagram <http://www.benplace.com/cooling_system_flow.htm>
of the flow (read his note at bottom about minor error in flow
diagram: water through left side jacket flows INTO the water pump, not
out as marked).

On 5/22/05, Don in North Carolina <Don_Dixon@bellsouth.net> wrote:
> I have a quick question for the coolant flow gurus out there.  Where does
> the front heater get it's coolant from?  Is it pulled off of the coolant
> lines that go to the radiator, or do coolant lines run all the way back to
> get coolant from the engine compartment coolant distributor?  This would be
> on my '88 Vanagon, BTW.  What I am trying to determine is if the coolant
> going to the front heater is before or after the thermostat...
> 
> Don in Reidsville, NC
> 1986 Kawasaki Concours
> 1988 Vanagon GL (Sylvia)
> "I reject your reality and substitute my own." - Adam Savage
>