I've had my '85 Vanagon GL for four years now, and continue to be baffled by
the heating system.  The first year we owned the van, we had little heat,
but I noticed that the temp gauge dropped at highway speed and replaced the
thermostat pronto.  We then had heat for another year and a half, then the
heat disappeared again.  Thermostat is working fine, I've bled the radiator
MANY times, and it's got a new water pump.

I've flushed the system a few times, run water through the front heater core
to flush it out, all to no avail.  My latest experiment was to tape over
most of the fresh air intake behind the grille to keep the core from being
flooded with too much cold air.  Not much improvement.

Here's the tricky part - some days it heats just great, other days nothing.
This problem is not predictable.  On the "no-heat" days, I do manage a
trickle of warm air from the rear core, on "heat" days, both heaters work
OK.

Early October in western Washington isn't cold, so if I'm unhappy with my
heat now, I know I'm going to be even less happy in January.  Any info would
be greatly appreciated.  The best I've found so far is a post in the
archives from 1995 that recommends flushing the cores with boiling caustic
solution.  I'm not sure I'm prepared for that!

TIA,

Randy, Carla & Anna Huyck
'75 Westy (waiting for an engine, then I can try the Eberspacher!)
'79 Mercedes 300D
'85 Vanagon
'90 Fox