ok to make a long story short, my parents were driving through wyoming on there way to idaho and the temp went up to approx 250 degrees. made it all the way to idaho with a/c off and temp hovering around 212 to 215 degrees. runs fine on flat ground with a/c on but once we started to head into the mountains temp shot up to 260 degrees, dash flashed change engine oil and shut off engine immediately all this happened going up hill and a/c on. pulled over and turned off car immediately. let it sit for a while and then headed back to dealership. dealership looked at it and said blown headgasket and 3800 dollars would fix it. well my parents were looking for a new car anyway and said i could keep it, do what i want with it, so i have a 97 deville to try to fix and make some money off of it. i know absolutely nothing about cadillacs, just want to know how easy it is to fix a headgasket or if anybody has any other ideas about what it is. the car seems to drive just fine around town with a/c on just dont go up any mountains. thank you.