Nindigully many years ago on an endevour car rally, was minus 4 or minus 5 (forget exactly which it was) the publican told us that morning whilst we were having brekky. Would have done a few similar temps on that trip out West that year.... recall waiting atleast 15 - 20 minutes for the heater to defrost the front windscreen one morning so we could drive off, ice was to thick to scrape from the windscreen that day.