So yesterday I let my truck (93 sierra 350 TBI) heat up for 20 minutes since it was -25 celsius with windchill, the drive to work was unusually long at an hour. Yet the temperature gauge didnt move up at all and there was NO warm air in the cabin at all, which made for a very very cold start to the day. Then on the way home from work, about 5 minutes into the commute the trucks temp gauge was climbing insanely fast and then it overheated and spilled coolant. At this point the overflow reservoir was full, coolant is pretty much brand new, engine only has 10,000 kms on it. I'm hoping that this is the thermostat? any help or advice?