Extreme cold caused thermostat problem

[azakram]

Last week -30F degree temp caused no heat inside the car. Later I took it to the mechanic and he said thermostat is out. and it is $500 job.
I changed that sucker some years back, it is under the intake manifold and difficult to take out.

I am thinking to change or flush the antifreeze, anyone had any luck with that?

[aleekat]

If the thermostat is stuck open, flushing etc won't do any good.

[Stealthee]

As aleekat said if it is a thermostat problem the only fix is to replace the thermostat. With the thermostat being stuck open the coolant can never reach operating temperature. Fresh coolant won't fix that.

[Blue Bowtie]

If the 'stat didn't close at -30, it's probably never going to close. A flush to clear it out would be nearly miraculous.

BTW - It was a few degrees cooler here, and my two daily drivers stayed very low on their temperature gauges, but still well above 160°F.