Re: Temp gauge rises - no cabin heat

John wrote:
> Here's the situation, looking for confirmation on my possible diagnosis
or a 
> point in another direction.
> 
> 1989 900 T
> Engine up to temperature and idling in a parking lot with the outside 
> temperature around 20 degrees F.  The temperature gauge starts climbing
and 
> at the same time the cabin heat starts blowing cold air.  Once we start 
> driving again the heat comes back and the temp gauge goes back to
normal.
> 
> Are we talking a bad thermostat here or am I way off base?

In my limited experience with an American car, this is caused by low 
coolant level.With the engine at idle, the level is too low to reach the 
heater core. As the RPMs come up, the water pump flogs the coolant more 
strongly, and some of it reaches the heater core inlet.

Possibly also the water pump itself - or the belt driving it.

Bill