Yup, that thermostat was overheated.... Something caused that thermostat to open too far.... The pellets inside the thermostat were overheated and the stat opened up too far, in an attempt to allow more flow to prevent overheating. But, something else has caused the overheating, p0ssibly not enough snow on coolers.... Was it hardpark like bigred said, or is waterpump belt slipping?? If those were all okay, better check top gaskets of engine. Did you check cylinders for any signs of coolant??? Any collapsed coolant hoses??