Q: What can cause heater to start blowing cold air and temperature to get really hot?

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I warmed up car this morning and we left. Then I had to wait 20 mins for school bus with car running and temp stayed normal. I got about 3 miles down the road and started up a steep hill when I noticed the heater was blowing cold air and car was very hot. I pulled over and turned off ignition. Could hear the gurgling noise a hot car makes and smell it was hot. Nothing had leaked out from it and I know it has antifreeze in it.

My car has 176785 miles.
My car has an automatic transmission.

Generally when the engine temperature climbs and the heater airflow turns cold, coolant has stopped circulating throughout the system. This can be due to a few things. The thermostat may have failed and is restricting coolant flow. The water pump impeller may have separated from the pulley shaft internally. The water pump can appear to be turning on the outside but the impeller may not be turning on the inside. Have the overheating condition checked immediately as continued driving can severely damage the engine.

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