DJC wrote:
On 22/12/17 14:34, ARW wrote:
De-icer these days only seems to work when it's above minus 1 deg
regardless of what it says on the tin.
During the recent cold spell I spayed de-icer on the windscreen, which
promptly froze making things worse. I wasn't below -2C.

The air temperature may be above -2 but how cold was the windscreen?

The problem with windscreens is that they face the sky. On a clear
night heat radiates from the glass into space, and that coming back is
minimal as space is about -270C. The screen can't get too cold as it
will absorb heat from the air, but it can be well below the air
temperature.

Was it an aerosol or spray bottle? I find the aerosol de-icers useless -
the aerosol cools the de-icer (which cools the windscreen) so much that
it adds ice to the windscreen rather than removing it. The spray
bottles don't have this issue as there's no propellant to cool the
spray.

Mike