We've had some pretty cold temps lately (single digit lows) and last Saturday I had the same experience as CoBeerToad. I had a hard time getting the cap off because it was frozen to the filler. I racked it up to condensation but was surprised at the amount of moisture. The filler neck wall had a thin layer of ice as well. Car is driven daily around 75 miles/day. 20K miles on the odometer.
