Chevrolet Repair: 2006 Impala LTZ 3.9 cooling fans run on, engine thermostat, upper radiator hose

Question
Hi, I bought LTZ with blown engine (no history) replaced engine with nice 50K. Runs great...temp gauge goes to middle (stays there) radiator fans turn on and then stay on until off with key and cool down..does not overheat. new AC Delco thermostat and water pump. no codes or trouble faults. Don't want this engine to fail because of this....not a normal fan cycle..once they turn on (and it is too soon) one click above middle on gauge they stay on temp on gauge does not move but fans continue to run and run driving steady
40 degree weather 10-20-30 miles without stopping fans continue running. When I get home fans still running but engine is not overheating. Upper radiator hose 190 degrees with contact thermometer. Good flow in radiator and system bled of air
fans thermostat working checked with meter..... pulled fuse for fans and fans goes off...I read in some GM forum engine thermostat could be stuck open and fools engine management because timed cycle to reach normal operational temp not reached

Answer
HI HARRY,I WOULD GET THIS ENGINE SCANNED FOR LIVE DATA. [NOT CODES] AND SEE WHAT THE PCM IS SEEING THE ENG TEMP AT. IF TEMP IS ABOUT 190 DEGREES ALL IS GOOD. IF HIGHER THEN THIS 190 THIS WOULD EXPLAIN WHY THE COOLING FANS STAY ON. TIME FOR A NEW ENGINE COOLANT TEMP SENSOR..MORE THEN LIKELY A RELAY IS BAD OR THE ENG TEMPERATURE SENSOR IS BAD THAT CONTROLS THESE FANS..IT MAY SEE THE TEMP HIGHER THEN NORMAL AND THIS WOULD KEEP THE COOLING FANS ON..SO I WOULD REPLACE THE COOLING FAN TEMP SENSOR WITH A GM SENSOR ONLY..SEE IF THIS WORKS AND FIND THE COOLING FAN RELAY UNDER THE HOOD FUSE BOX AND SWITCH THIS RELAY WITH ANOTHER REALY OF THE SAME STYLE AND SEE IF THIS TAKES CAR OF YOUR PROBLEM. [[YOU COULD JUST FIND THE SAME RELAY IN THE FUSE BOX AND SWITCH IT AROUND.]] LET ME KNOW HOW THIS WORKS FOR YOU AND GET BACK TO ME IF NEEDED. GOOD LUCK TOM..