Feel the upper radiator hose after the engine has been running a while. It should be too hot to hold onto for very long. If it is not, suspect the thermostat. If it is, feel the heater hoses. They should be just as hot. If they are not, suspect the heater core is plugged or there's a water valve inline with one of those hoses that isn't opening up when heat is selected. If the heater hoses are hot, suspect a problem with the actuator or cable for the temperature door in the heater box.
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Wednesday, October 8th, 2014 AT 1:05 AM