Went out earlier only did maybe 5 miles stopped for a dog walk, on the way back the temperature gauge went low and the air coming out of vents was much hotter than usual. No warnings for low coolant or overheating, still coolant in header tank but top rad hose feels like it has no coolant in? Usually wouldn't quite have got fully warm on the same journey. Anyone had similar problem? It's not had thermostat replaced yet.