I iike that answer.  I'm pretty sure I didn't drive with a bad thermostat, low coolant and air pockets for all 16 years of van ownership.  Maybe 10 years but not all 16 :)

Try your rear heater - it will likely blow heat at idle (mine does).  -30 weather can take a lot of heat out of coolant over 6 feet of travel.

Jeff

On 2010-01-06, at 1:13 PM, Don Spence wrote:

> Think about it. The engine is way in the back, the heater is way in
> the front.  The transfer tubes from rear to front are exposed to the
> elements and share their captive heat with the radiator. (which
> transfers heat to the external air mass.) So, the heater core is
> disadvantaged from the beginning.
> 
> The heater has a fan blowing cold air across the heater core
> (assuming you are set to outside air and not recirculating inside
> cabin air which would slightly lessen the situation).
> 
> At idle the water pump is providing minimum flow hence minimum hot
> water available for heat transfer in the heater core. Now add a
> "tired" pump with worn or eroded vanes and you get even less flow and
> less heat to transfer.  If the fluid is barely moving through the
> core the latter will quickly cool and blow cold.  Pick up the revs
> and you do two things. Add more fuel to the fire (gasoline) and pump
> hot fluid faster and in greater volume. Voila, Heat.
> 
> It's very common. My 3.3 L chrysler V6 van blows cool at idle
> (172,000 kms) as does my Mazda 2.2 turbo (282,000 kms) when it's
> below -20 C. ( Which it is today)
> 
> 
> 
> On 6-Jan-10, at 11:31 AM, mcneely4@cox.net wrote:
> 
>> Someone else suggested the no heat when stopped situation is normal
>> during cold weather because the coolant temp drops.  In my
>> experience, and that of a good many others, Vanagon usually runs
>> cooler when moving than when idling, due to increased air flow
>> through the radiator.  But, if the water pump is moving fluid
>> poorly, perhaps the radiator and coolant pipes would have stagnant
>> coolant.
>> 
>> 
>> On Wed, Jan 6, 2010 at 12:13 PM, Don Spence wrote:
>> 
>>> Tired water pump.
>>> 
>>> 
>>> On 6-Jan-10, at 8:38 AM, Automatic digest processor wrote:
>>> 
>>>> No heat at stoplights.