Sled is overheating in 12 inches powder equally as quickly as the trail. Takes 1.5 miles on the trail to have the engine shut down the sled due to excessive heat, at least as measured by temp sensor. Heat exchangers are warming up as they did previously. Thermostat was changed prior to trip since sled was getting warmer than our other XML. Now it is completely unrideable and towed out of Cooke City. Was run with front end elevated 4-5 feet without air bubbles coming out reservoir. Any suggestions? Coolant is circulating so pump seems to be functioning. Dropping off at dealer again tonight. Worked great previously except running warmer but was able to be cooled in powder in 60 seconds prior to thermostat change.