It better not go to 250 degrees. If it does, you have a problem. Dash gauges are notoriously inaccurate. They often read lower in cold weather. If you want a more accurate reading to know what temperature the engine is running at, use a scanner that displays live data and read the temperature the Engine Computer is seeing. If it's close to where it should be; around 190 to 215 degrees or so, you will get nice hot air from the heater.