Could staring a cold engine in -20 degrees that does not have a block heater cause any damage?
It's a funny thing... As celly said, lots of people never use one, even in areas where it is cold all winter -- and certainly cold enough to warrant a block heater -- but I attribute that to people being somewhat ignorant about cars no matter where they live.
IMO, and as a professional ASE certified mechanic and life-long resident of Wisconsin until the last 8 years, -20 and below DO damage engines and other componets of automobiles. Your oil simply cannot circulate at that temprature - it will NOT suck up the pick up tube of the oil pump, and if it does get picked up, it is too thick to make it through the oil galleries of the engine until it begins to warm up. For that reason, I switched to synthetic oils in ALL the areas that took any type of oil or grease in my own vehicles and never looked back. The syntetics are NIGHT AND DAY difference in really cold weather. They flow normally until well below -50 which is going to handle most of the severe cold weather times that most people in most places in North America are going to face.
I have watched people blow their oil filters right off the engine trying to "rev up" a slow starting engine or trying to get a cold car to move off the spot. Some engines are notorious for blowing out the oil pump drive shaft, and in the engines I built, I would replace the factory plastic type drives (in the engines that had them) with a better steel drive and/or a high performance part that was stronger than stock.
I also ran at least a 1000 cold-cranking amp battery no matter what the car needed in the warmer months. Of course, block heaters were part of my plan as well, and my cars always got "plugged in" when the temps dropped below zero. I also have a magnetic oil pan heater that really helped all the neighbor's cars that didnt' start like mine did...
My "winter kit" for all my cars and trucks consisted of:
-Synthetic oils all around
-1000 CCA battery and GOOD cables (Good meaning as heavy as I could find or make!)
-Proper tune up
-Jumper Cables in all the cars
-A can of WD 40 (works great for drying out wires that have become sno-packed when busting drifts - but hardly anything else)
-A can of starting fluid
-"Red" Heat (or any ISO- alcohol gasoline dryer -- the "Yellow" Heat products and their kind don't really do much)
-Keep the gas tank full as possible in very cold conditions - (top it off every day if you can - for a number of reasons - not the least of which being the ability to keep the car idling to stay warm in case you went off the road somewhere due to snow or ice conditions)
-Some "traction adding" device - usually an old rubber/carpet car mat (the kind with the spikes seems to work well - and a 50# bag or 2 of cat litter in the trunk for weight and for spreading on snow/ice for better traction when stuck)
-A Tow strap of some kind - even a cheapy tow ropw for cars
-A blanket, extra hats, gloves, scarf, etc just for emergency
-A lighter (carry it in your pocket for thawing frozen locks and keep a spare in the car)
-A small shovel - preferably with flat blade - which works MUCH better than a pointed spade for snow or ice work
-a GOOD window scraper
-And in freezing rain conditions, ISOPROPYL alcohol in the windshield washer bottles straight up. It's the only thing that will keep up with a good dose of freezing rain - and then barely.
If all that sounds rather severe, know that I was a professional driver and I drove between 500 and 700 miles a day - every day - no matter what, and I never missed a day for 11 years because I couldn't go when I needed to or wanted to -- unlike MANY of the other idiots that never did learn, even though it gets to be winter every year like clockwork.
Feel free to ask me other questions about winter driving tips, etc. I have logged over 1.5 million miles without much in the way of major mishaps in some of the worst winter driving territory on earth and I know what works and what doesn't. Hope this helps someone else prepare.