Hardly any heat at below -20c

[Mellemel]

Anyone else have hardly any heat blowing from the vents when it's below -20c ?
It blows hot up to about -10c however !
Just wondering. Maybe I need to flush out the heater core or something this summer.

 

[wc11]

Flush and replace the thermostat.

 

[AZ4Running]

It does not get that cold where i live but at 30F my heater blows warmish. I need to flush out my heater core. You should be doing that as well to clear out any crap plugging up the heater core.

 

[Mellemel]

Heater core flush it is then. Thx.