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Q: Engine overheats, heater blows out cold air, coolant boils in radiator

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My engine overheats and the coolant boils and the heater in my truck blows straight cold air. I at one point drained my coolant completely with the plug on the bottom of the radiator and seen that it was dirty. I'm wondering what it could be? Do a thermostat replacement? Do a radiator complete flush? Or do both thermostat replacement and complete radiator flush?

My car has 177438 miles.
My car has an automatic transmission.

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