Poor heat at idle??

[charlie8]

Hi friends,
My 2005 XC70 seems to lack heat when the engine is idling. When the engine is hot and I'm driving, there is plenty of heat coming out of the vents, but when I stop and idle, the air temp drops to cool. Is this a design flaw in these models where the slower speed of the water pump is not pushing water up through the heater core, or is it possible I have some air trapped in the heater core that is causing this. Does anyone else have this condition of poor heat at idle? Any other ideas on what is causing this??
Thanks

[mpitts]

I have the same problem. Noticed it today since I needed heat as the temp. was -15F this AM.

[GearheadNY.com]

Not too sure about how volvo works the heat in these things, but from experience there are a few different situatiions that cause this problem assuming you're cooling system is working properly.

1: Thermostat is going south
2: Coolant level is low
3: heater core is clogged/clogging - poor/low flow

A more rare event(seen commonly with VW and BMW) is the impeller on the water pump goes out because it's plastic. Not too sure the Volvo ones are plastic though.