Running the heater (on any liquid cooled engine with a heater core) is a classic way to help to cool an overheated engine.  Yes, the heater will do that.  Shedding heat from the cooling system to the interior of the vehicle is how it works.  At normal operating temperatures it should not make much difference, since the thermostat should help keep the temperature up (that's what it is for).  So, maybe you have a thermostat that is opening at a lower than normal temperature.   mcneely

---- Steve Williams <steve@WILLIAMSITCONSULTING.COM> wrote:
> Hi,
>
> Driving my 1991 Westfalia, I see a phenomem that I do not understand.
>
> When my van is up to temperature, the needle sits approximately where
> everyone describes, just below the LED.
>
> On a cool day (around freezing yesterday), if I turn on the front
> heater, the temperature guage goes down.
>