It sounds to me like your water pump isn't pumping enough at idle. When you speed up, it pumps more though the system, warming up your heater with fresh hot coolant. Others would know a lot better than I, but it might be time for a new water pump - or at least a thorough inspection??

-Ben

> Date: Wed, 12 Dec 2007 14:12:26 -0800
> From: matt@SNOOKSBAND.COM
> Subject: heater, interrupted
> To: vanagon@GERRY.VANAGON.COM
> 
> Another heater question.  Curiosity, I guess.
> 
> My heaters seem to work.  I have some leak in the back that I can smell
> briefly whenever I turn on the rear fan.  Other than that, all is well.
> 
> But!  When I pull up to an intersection with a light or a stop sign, the
> temperature of the heated air starts dropping immediately.  If I sit for
> more than a minute or so, it seems to be blowing room temperature air.  Not
> as cold as what's outside, but not necessarily heated, either.
> 
> Meanwhile, when driving the temperature gauge stays down near the bottom
> mark.  When I stop and idle, that needle will eventually start to climb,
> 'til it nearly touches the warning light.
> 
> Then, when I take off again, the temperature gauge goes back down, and the
> temperature of the heater air goes back up to nice and toasty.
> 
> What's up with all this temperature change?
> 
> Matt

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