Why is my car running hot but heater blowing cold air.?

2001 chevy impala 3.4L. The car is running hot but the heater blows cold air.I changed the t thermostat but that didn't solve the problem. Please help me solve this problem or direct me to a very helpful website. if it help my top hose is hot while my bottom hose is cold also my radiator cap be cold when the... show more 2001 chevy impala 3.4L. The car is running hot but the heater blows cold air.I changed the t thermostat but that didn't solve the problem. Please help me solve this problem or direct me to a very helpful website. if it help my top hose is hot while my bottom hose is cold also my radiator cap be cold when the car is over heating. I get no steam or bubbling sound just temp gauge going to over heated level. Thanks in advance
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