Sometimes my autostop doesn't work even with 4 or 5 bars on the temp meter. This has happened with temps below 10F outside. However, it's not always true -- sometimes it does work to my pleasant surprise.

In general, I expect the autostop to work when the temperature is 30s or higher outside, and I just HOPE that it works when it's colder. (We've had around 0 degree weather in the mornings the past week, which is evident in my last tank's mpg average).