Car deicier is not an approved fluid for use on an aircraft, it is also not an anti ice, nor do you know what its holdover time is. It may well get rid of the ice but you are introducing a water based fluid onto the wing and you have no idea what will happen to that fluid in sub zero temperatures apart from at some stage it will refreeze.
Perfectly correct, but on a practical basis will do a proper job of dissolving the frost. Remember that after application the stuff has to evaporate, aided perhaps with the spongy side of your windshield squeegee.
Once the wing is clean and dry with no ice in nooks and crannies, who cares how it got that way.
On a nice morning after a frosty night, this approach can get you an properly clean wing, but if there's freezing precip, I'd be turning around before I got to the airport.
Mechanical scraping between the rivet lines got me an interesting low level excursion over the ravine at the end of the runway until I had another 15 kts or so. After that I took to carrying windshield washer fluid.