When I lived here 13 years ago it got down to -40 f and I just wanted to see if my 68 dart would start and it fired right up after I brought the battery in to warm up for an hour. Yes it always had 20-50 in it. My 68 cuda started up the other day at -20 f but I run 10-30 in it and my 00 durango, my 91 dak started and it has 20-50 because it burns so much.