I'm pretty sure this is an urban legend, albeit a funny one. On Mythbusters, they covered this, by getting several canisters of various "whoppin' biscuits" and putting them on a car rear window package deck, which they then put under heat lamps to get the temps up. I think they called it plausible, but not confirmed, and the temperature in the car had to get up to around 150 degrees before the cans popped. Pretty funny to watch.
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