10 minutes isn't enough in REALLY cold weather IME.. I'm talking less than about minus 5C, when you need to start the engine, then spray de-icer, scrape the ice off ALL windows, and wait until the engine is warm enough to blow warm air onto the inside of the windscreen. Otherwise the condensation caused by your very presence when you sit in the car will freeze on the inside of the screen. Unless of course you've got a new fankled car with a heated windscreen, which, as the proud owner of a 10 year old Toyota Corolla I don't have
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