Hey all, I have an 04 trail blazer. Yesterday a high coolant temperature warning message came on and the temp gauge had moved from 210(normal) to 260 (red zone). I shut off the engine and checked under the hood. Coolant reservoir was full. No apparent leaks anywhere. After cooling down I removed radiator cap, radiator full. I restarted and drove home, about 20 minutes, with no problem. Left engine idling for about 30 minutes. No problem, normal temperature, cooling fan running. Any thoughts?