[David in San Antonio]

The blanket on the hood always makes me wonder how much insulation that actually provides to slow the migration of the engine’s heat when it’s shut off. Blankets help keep mammals warm because we generate heat. Car engines only generate heat when running.
In Minnesota it was common practice when very cold to go outside and start your car at least once during the work day, and right before going to sleep at night. Block heaters were common enough to not merit discussion. One time when it was about 20 below zero F (50 degrees hotter in your freezer) when I finally got my Volvo running in the morning I just left it running the entire work day. Doors unlocked because 1. They can easily freeze shut and 2. It was Chaska Minnesota so I didn’t expect any shenanigans. When I got back to the car it was nice and toasty, the gas gauge had barely moved, and there was a half inch fissure in the dashboard running from the base of the windshield down to the radio. Oh, and the plastic floor trays meant to protect the carpeting had curled up around the edges. My conclusion: metal is hardier than plastic.