Q: Heater blows hot for 10 minutes, then it blows cold.

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When i run my heater it blows hot for 10 minutes or so, then it blows cold air out of the defrost vents. If i turn it off for about 10 minutes it will blow hot again for again about 10 minutes and then blows cold again out of the defrost vents. If I am running defrost it is basically the same hot for a little while and then cold untill i turn it off for a little bit.

My car has 118000 miles.
My car has an automatic transmission.

Hello, thanks for writing in. This problem could be either an engine thermostat that is not keeping the engine at a constant running temperature (temp gauge steady in the center), or the heater control valve or controls are malfunctioning not allowing engine coolant into the heater core (passenger compartment). It is also possible that the heater controls are allowing cold outside air to "blend" with heated air by not closing one of the ducts in the HVAC unit. I would recommend having a heater inspection completed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.

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